gocql

https://pkg.go.dev/github.com/gocql/gocql
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### Install gocql with go get

Source: https://pkg.go.dev/github.com/gocql/gocql

Install the gocql package using the go get command. This is the standard installation method for Go modules.

```bash
go get github.com/gocql/gocql
```

--------------------------------

### MapScanCAS example

Source: https://pkg.go.dev/github.com/gocql/gocql

Demonstrates executing a single-statement lightweight transaction with MapScanCAS. Assumes a keyspace and table are set up as described in the comment. Shows the output of the example.

```go
package main

import (
	"context"
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.my_lwt_table(pk int, version int, value text, PRIMARY KEY(pk));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	err = session.Query("INSERT INTO example.my_lwt_table (pk, version, value) VALUES (?, ?, ?)",
		1, 1, "a").WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}
	m := make(map[string]interface{})
	applied, err := session.Query("UPDATE example.my_lwt_table SET value = ? WHERE pk = ? IF version = ?",
		"b", 1, 0).WithContext(ctx).MapScanCAS(m)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(applied, m)

	var value string
	err = session.Query("SELECT value FROM example.my_lwt_table WHERE pk = ?", 1).WithContext(ctx).
		Scan(&value)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(value)

	m = make(map[string]interface{})
	applied, err = session.Query("UPDATE example.my_lwt_table SET value = ? WHERE pk = ? IF version = ?",
		"b", 1, 1).WithContext(ctx).MapScanCAS(m)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(applied, m)

	var value2 string
	err = session.Query("SELECT value FROM example.my_lwt_table WHERE pk = ?", 1).WithContext(ctx).
		Scan(&value2)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(value2)
	// false map[version:1]
	// a
	// true map[]
	// b
}
```

```text
Output:
```

--------------------------------

### ExampleUDTMarshaler implementation

Source: https://pkg.go.dev/github.com/gocql/gocql

Complete example demonstrating how to implement the UDTMarshaler interface. It defines a MyUDTMarshaler struct with MarshalUDT method and inserts a UDT value into a Cassandra table. The example assumes a specific CQL setup with keyspace 'example', type 'my_udt', and table 'my_udt_table'.

```go
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40
 * Copyright (c) 2016, The Gocql authors,
 * provided under the BSD-3-Clause License.
 * See the NOTICE file distributed with this work for additional information.
 */

package main

import (
	"context"
	"log"

	gocql "github.com/gocql/gocql"
)

// MyUDTMarshaler implements UDTMarshaler.
type MyUDTMarshaler struct {
	fieldA string
	fieldB int32
}

// MarshalUDT marshals the selected field to bytes.
func (m MyUDTMarshaler) MarshalUDT(name string, info gocql.TypeInfo) ([]byte, error) {
	switch name {
	case "field_a":
		return gocql.Marshal(info, m.fieldA)
	case "field_b":
		return gocql.Marshal(info, m.fieldB)
	default:
		// If you want to be strict and return error un unknown field, you can do so here instead.
		// Returning nil, nil will set the value of unknown fields to null, which might be handy if you want
		// to be forward-compatible when a new field is added to the UDT.
		return nil, nil
	}
}

// ExampleUDTMarshaler demonstrates how to implement a UDTMarshaler.
func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create type example.my_udt (field_a text, field_b int);
	create table example.my_udt_table(pk int, value frozen<my_udt>, PRIMARY KEY(pk));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	value := MyUDTMarshaler{
		fieldA: "a value",
		fieldB: 42,
	}
	err = session.Query("INSERT INTO example.my_udt_table (pk, value) VALUES (?, ?)",
		1, value).WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}
}
```

--------------------------------

### Query Cassandra with gocql and print results

Source: https://pkg.go.dev/github.com/gocql/gocql

This example connects to a Cassandra cluster, runs three SELECT queries, and prints the results with column names and types. It assumes a keyspace 'example' with tables 'table1' and 'table2' as described in the CQL comments. The output shows the query results with column types and values.

```go
package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"reflect"
	"text/tabwriter"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.table1(pk text, ck int, value1 text, value2 int, PRIMARY KEY(pk, ck));
	insert into example.table1 (pk, ck, value1, value2) values ('a', 1, 'b', 2);
	insert into example.table1 (pk, ck, value1, value2) values ('c', 3, 'd', 4);
	insert into example.table1 (pk, ck, value1, value2) values ('c', 5, null, null);
	create table example.table2(pk int, value1 timestamp, PRIMARY KEY(pk));
	insert into example.table2 (pk, value1) values (1, '2020-01-02 03:04:05');
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	printQuery := func(ctx context.Context, session *gocql.Session, stmt string, values ...interface{}) error {
		iter := session.Query(stmt, values...).WithContext(ctx).Iter()
		fmt.Println(stmt)
		w := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ',
			0)
		for i, columnInfo := range iter.Columns() {
			if i > 0 {
				fmt.Fprint(w, "\t| ")
			}
			fmt.Fprintf(w, "%s (%s)", columnInfo.Name, columnInfo.TypeInfo)
		}

		for {
			rd, err := iter.RowData()
			if err != nil {
				return err
			}
			if !iter.Scan(rd.Values...) {
				break
			}
			fmt.Fprint(w, "\n")
			for i, val := range rd.Values {
				if i > 0 {
					fmt.Fprint(w, "\t| ")
				}

				fmt.Fprint(w, reflect.Indirect(reflect.ValueOf(val)).Interface())
			}
		}

		fmt.Fprint(w, "\n")
		w.Flush()
		fmt.Println()

		return iter.Close()
	}

	ctx := context.Background()

	err = printQuery(ctx, session, "SELECT * FROM table1")
	if err != nil {
		log.Fatal(err)
	}

	err = printQuery(ctx, session, "SELECT value2, pk, ck FROM table1")
	if err != nil {
		log.Fatal(err)
	}

	err = printQuery(ctx, session, "SELECT * FROM table2")
	if err != nil {
		log.Fatal(err)
	}
	// SELECT * FROM table1
	// pk (varchar) | ck (int) | value1 (varchar) | value2 (int)
	// a            | 1        | b                | 2
	// c            | 3        | d                | 4
	// c            | 5        |                  | 0
	//
	// SELECT value2, pk, ck FROM table1
	// value2 (int) | pk (varchar) | ck (int)
	// 2            | a            | 1
	// 4            | c            | 3
	// 0            | c            | 5
	//
	// SELECT * FROM table2
	// pk (int) | value1 (timestamp)
	// 1        | 2020-01-02 03:04:05 +0000 UTC
}
```

--------------------------------

### gocql UDT Struct Example

Source: https://pkg.go.dev/github.com/gocql/gocql

Complete example showing how to use a user-defined type as a struct with gocql. It assumes a keyspace with a UDT and table created via the CQL statements in the comment. The example inserts a MyUDT value and then selects it back, printing the fields.

```go
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40
 * Copyright (c) 2016, The Gocql authors,
 * provided under the BSD-3-Clause License.
 * See the NOTICE file distributed with this work for additional information.
 */

package main

import (
	"context"
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

type MyUDT struct {
	FieldA string `cql:"field_a"`
	FieldB int32  `cql:"field_b"`
}

// Example_userDefinedTypesStruct demonstrates how to work with user-defined types as structs.
// See also examples for UDTMarshaler and UDTUnmarshaler if you need more control/better performance.
func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create type example.my_udt (field_a text, field_b int);
	create table example.my_udt_table(pk int, value frozen<my_udt>, PRIMARY KEY(pk));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	value := MyUDT{
		FieldA: "a value",
		FieldB: 42,
	}
	err = session.Query("INSERT INTO example.my_udt_table (pk, value) VALUES (?, ?)",
		1, value).WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}

	var readValue MyUDT

	err = session.Query("SELECT value FROM example.my_udt_table WHERE pk = 1").WithContext(ctx).Scan(&readValue)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(readValue.FieldA)
	fmt.Println(readValue.FieldB)
	// a value
	// 42
}

```

--------------------------------

### SimpleRetryPolicy usage examples

Source: https://pkg.go.dev/github.com/gocql/gocql

Examples of assigning the retry policy to a cluster and to a query.

```go
//Assign to the cluster
cluster.RetryPolicy = &gocql.SimpleRetryPolicy{NumRetries: 3}

//Assign to a query
query.RetryPolicy(&gocql.SimpleRetryPolicy{NumRetries: 1})
```

--------------------------------

### ExampleSession_MapExecuteBatchCAS demonstrates batch lightweight transaction

Source: https://pkg.go.dev/github.com/gocql/gocql

Full example showing how to execute a batch lightweight transaction using MapExecuteBatchCAS. It assumes a keyspace and table are set up with the provided CQL. The example inserts initial rows, then executes a batch with conditional updates, printing the applied status and scanned results.

```go
package main

import (
	"context"
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.my_lwt_batch_table(pk text, ck text, version int, value text, PRIMARY KEY(pk, ck));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	err = session.Query("INSERT INTO example.my_lwt_batch_table (pk, ck, version, value) VALUES (?, ?, ?, ?)",
		"pk1", "ck1", 1, "a").WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}

	err = session.Query("INSERT INTO example.my_lwt_batch_table (pk, ck, version, value) VALUES (?, ?, ?, ?)",
		"pk1", "ck2", 1, "A").WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}

	executeBatch := func(ck2Version int) {
		b := session.NewBatch(gocql.LoggedBatch)
		b.Entries = append(b.Entries, gocql.BatchEntry{
			Stmt: "UPDATE my_lwt_batch_table SET value=? WHERE pk=? AND ck=? IF version=?",
			Args: []interface{}{"b", "pk1", "ck1", 1},
		})
		b.Entries = append(b.Entries, gocql.BatchEntry{
			Stmt: "UPDATE my_lwt_batch_table SET value=? WHERE pk=? AND ck=? IF version=?",
			Args: []interface{}{"B", "pk1", "ck2", ck2Version},
		})
		m := make(map[string]interface{})
		applied, iter, err := session.MapExecuteBatchCAS(b.WithContext(ctx), m)
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println(applied, m)

		m = make(map[string]interface{})
		for iter.MapScan(m) {
			fmt.Println(m)
			m = make(map[string]interface{})
		}

		if err := iter.Close(); err != nil {
			log.Fatal(err)
		}
	}

	printState := func() {
		scanner := session.Query("SELECT ck, value FROM example.my_lwt_batch_table WHERE pk = ?", "pk1").
			WithContext(ctx).Iter().Scanner()
		for scanner.Next() {
			var ck, value string
			err = scanner.Scan(&ck, &value)
			if err != nil {
				log.Fatal(err)
			}
			fmt.Println(ck, value)
		}
		if err := scanner.Err(); err != nil {
			log.Fatal(err)
		}
	}

	executeBatch(0)
	printState()
	executeBatch(1)
	printState()

	// false map[ck:ck1 pk:pk1 version:1]
	// map[[applied]:false ck:ck2 pk:pk1 version:1]
	// ck1 a
	// ck2 A
	// true map[]
	// ck1 b
	// ck2 B
}
```

--------------------------------

### Query.Release method signature and example

Source: https://pkg.go.dev/github.com/gocql/gocql

Releases a query back into a pool of queries. Released Queries cannot be reused. The example shows creating a query, executing it, and releasing it.

```go
func (q *Query) Release()
```

```go
qry := session.Query("SELECT * FROM my_table")
qry.Exec()
qry.Release()
```

--------------------------------

### Example: Handle Null Values with Scanner

Source: https://pkg.go.dev/github.com/gocql/gocql

Shows how to scan rows into a *string pointer to distinguish null from empty string. Assumes a keyspace 'example' with table 'stringvals' containing rows with null, empty, and 'hello' values. Outputs 'Row 1 is null', 'Row 2 is ""', and 'Row 3 is "hello"'.

```go
package main

import (
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.stringvals(id int, value text, PRIMARY KEY(id));
	insert into example.stringvals (id, value) values (1, null);
	insert into example.stringvals (id, value) values (2, '');
	insert into example.stringvals (id, value) values (3, 'hello');
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()
	scanner := session.Query(`SELECT id, value FROM stringvals`).Iter().Scanner()
	for scanner.Next() {
		var (
			id  int32
			val *string
		)
		err := scanner.Scan(&id, &val)
		if err != nil {
			log.Fatal(err)
		}
		if val != nil {
			fmt.Printf("Row %d is %q\n", id, *val)
		} else {
			fmt.Printf("Row %d is null\n", id)
		}

	}
	err = scanner.Err()
	if err != nil {
		log.Fatal(err)
	}
	// Row 1 is null
	// Row 2 is ""
	// Row 3 is "hello"
}

```

--------------------------------

### Example: Implementing UDTMarshaler

Source: https://pkg.go.dev/github.com/gocql/gocql

ExampleUDTMarshaler demonstrates how to implement a UDTMarshaler. It shows how to marshal UDT fields to bytes and insert them into a Cassandra table.

```APIDOC
## Example: Implementing UDTMarshaler

### Description
ExampleUDTMarshaler demonstrates how to implement a UDTMarshaler. It shows how to marshal UDT fields to bytes and insert them into a Cassandra table.

### Example Code
```go
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40
 * Copyright (c) 2016, The Gocql authors,
 * provided under the BSD-3-Clause License.
 * See the NOTICE file distributed with this work for additional information.
 */

package main

import (
	"context"
	"log"

	gocql "github.com/gocql/gocql"
)

// MyUDTMarshaler implements UDTMarshaler.
type MyUDTMarshaler struct {
	fieldA string
	fieldB int32
}

// MarshalUDT marshals the selected field to bytes.
func (m MyUDTMarshaler) MarshalUDT(name string, info gocql.TypeInfo) ([]byte, error) {
	switch name {
	case "field_a":
		return gocql.Marshal(info, m.fieldA)
	case "field_b":
		return gocql.Marshal(info, m.fieldB)
	default:
		// If you want to be strict and return error un unknown field, you can do so here instead.
		// Returning nil, nil will set the value of unknown fields to null, which might be handy if you want
		// to be forward-compatible when a new field is added to the UDT.
		return nil, nil
	}
}

// ExampleUDTMarshaler demonstrates how to implement a UDTMarshaler.
func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create type example.my_udt (field_a text, field_b int);
	create table example.my_udt_table(pk int, value frozen<my_udt>, PRIMARY KEY(pk));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	value := MyUDTMarshaler{
		fieldA: "a value",
		fieldB: 42,
	}
	err = session.Query("INSERT INTO example.my_udt_table (pk, value) VALUES (?, ?)",
		1, value).WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}
}
```

### Output
(No output is shown in the source.)
```

--------------------------------

### Basic gocql example: connect, insert, query, and scan

Source: https://pkg.go.dev/github.com/gocql/gocql

Shows how to connect to a Cassandra cluster, insert a tweet, query with a secondary index, and iterate over results using a scanner. Assumes a keyspace and table are set up as described in the comments.

```go
package main

import (
	"context"
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.tweet(timeline text, id UUID, text text, PRIMARY KEY(id));
	create index on example.tweet(timeline);
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.Consistency = gocql.Quorum
	// connect to the cluster
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	// insert a tweet
	if err := session.Query(`INSERT INTO tweet (timeline, id, text) VALUES (?, ?, ?)`,
		"me", gocql.TimeUUID(), "hello world").WithContext(ctx).Exec(); err != nil {
		log.Fatal(err)
	}

	var id gocql.UUID
	var text string

	/* Search for a specific set of records whose 'timeline' column matches
	 * the value 'me'. The secondary index that we created earlier will be
	 * used for optimizing the search */
	if err := session.Query(`SELECT id, text FROM tweet WHERE timeline = ? LIMIT 1`,
		"me").WithContext(ctx).Consistency(gocql.One).Scan(&id, &text); err != nil {
		log.Fatal(err)
	}
	fmt.Println("Tweet:", id, text)
	fmt.Println()

	// list all tweets
	scanner := session.Query(`SELECT id, text FROM tweet WHERE timeline = ?`,
		"me").WithContext(ctx).Iter().Scanner()
	for scanner.Next() {
		err = scanner.Scan(&id, &text)
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println("Tweet:", id, text)
	}
	// scanner.Err() closes the iterator, so scanner nor iter should be used afterwards.
	if err := scanner.Err(); err != nil {
		log.Fatal(err)
	}
	// Tweet: cad53821-3731-11eb-971c-708bcdaada84 hello world
	//
	// Tweet: cad53821-3731-11eb-971c-708bcdaada84 hello world
	// Tweet: d577ab85-3731-11eb-81eb-708bcdaada84 hello world
}
```

--------------------------------

### gocql batch example: execute a batch of statements

Source: https://pkg.go.dev/github.com/gocql/gocql

Demonstrates how to create and execute an unlogged batch of INSERT statements using gocql. Assumes a keyspace and table are set up as described in the comments.

```go
package main

import (
	"context"
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.batches(pk int, ck int, description text, PRIMARY KEY(pk, ck));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	b := session.NewBatch(gocql.UnloggedBatch).WithContext(ctx)
	b.Entries = append(b.Entries, gocql.BatchEntry{
		Stmt:       "INSERT INTO example.batches (pk, ck, description) VALUES (?, ?, ?)",
		Args:       []interface{}{1, 2, "1.2"},
		Idempotent: true,
	})
	b.Entries = append(b.Entries, gocql.BatchEntry{
		Stmt:       "INSERT INTO example.batches (pk, ck, description) VALUES (?, ?, ?)",
		Args:       []interface{}{1, 3, "1.3"},
		Idempotent: true,
	})
	err = session.ExecuteBatch(b)
	if err != nil {
		log.Fatal(err)
	}

	scanner := session.Query("SELECT pk, ck, description FROM example.batches").Iter().Scanner()
	for scanner.Next() {
		var pk, ck int32
		var description string
		err = scanner.Scan(&pk, &ck, &description)
		if err != nil {
			log.Fatal(err)
		}
		fmt.Println(pk, ck, description)
	}
	// 1 2 1.2
	// 1 3 1.3
}
```

--------------------------------

### Correct keyspace configuration before session creation

Source: https://pkg.go.dev/github.com/gocql/gocql

Example of correct usage: set the cluster.Keyspace before creating the session. This is the only way to define the default keyspace.

```go
	cluster := gocql.NewCluster("192.168.1.1", "192.168.1.2", "192.168.1.3")
	cluster.Keyspace = "example"
	...
	session, err := cluster.CreateSession()
```

--------------------------------

### ConstantReconnectionPolicy usage example

Source: https://pkg.go.dev/github.com/gocql/gocql

Example of setting a constant reconnection policy on a cluster with 10 max retries and an 8-second interval.

```go
cluster.ReconnectionPolicy = &gocql.ConstantReconnectionPolicy{MaxRetries: 10, Interval: 8 * time.Second}
```

--------------------------------

### Example: Manual Paging with PageState

Source: https://pkg.go.dev/github.com/gocql/gocql

Demonstrates manual paging using PageSize and PageState. Uses ProtoVersion 4 and PageSize(2) for demonstration; default page size is 5000. Output shows page state byte slices and row order.

```go
package main

import (
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.itoa(id int, description text, PRIMARY KEY(id));
	insert into example.itoa (id, description) values (1, 'one');
	insert into example.itoa (id, description) values (2, 'two');
	insert into example.itoa (id, description) values (3, 'three');
	insert into example.itoa (id, description) values (4, 'four');
	insert into example.itoa (id, description) values (5, 'five');
	insert into example.itoa (id, description) values (6, 'six');
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	var pageState []byte
	for {
		// We use PageSize(2) for the sake of example, use larger values in production (default is 5000) for performance
		// reasons.
		iter := session.Query(`SELECT id, description FROM itoa`).PageSize(2).PageState(pageState).Iter()
		nextPageState := iter.PageState()
		scanner := iter.Scanner()
		for scanner.Next() {
			var (
				id          int
				description string
			)
			err = scanner.Scan(&id, &description)
			if err != nil {
				log.Fatal(err)
			}
			fmt.Println(id, description)
		}
		err = scanner.Err()
		if err != nil {
			log.Fatal(err)
		}
		fmt.Printf("next page state: %+v\n", nextPageState)
		if len(nextPageState) == 0 {
			break
		}
		pageState = nextPageState
	}
	// 5 five
	// 1 one
	// next page state: [4 0 0 0 1 0 240 127 255 255 253 0]
	// 2 two
	// 4 four
	// next page state: [4 0 0 0 4 0 240 127 255 255 251 0]
	// 6 six
	// 3 three
	// next page state: [4 0 0 0 3 0 240 127 255 255 249 0]
	// next page state: []
}

```

--------------------------------

### Consistency.String method signature

Source: https://pkg.go.dev/github.com/gocql/gocql

Method to get string representation of Consistency.

```go
func (c Consistency) String() string
```

--------------------------------

### Configure TLS with SslOptions and EnableHostVerification

Source: https://pkg.go.dev/github.com/gocql/gocql

Example of setting SslOptions with EnableHostVerification set to true. Note that SslOptions is insecure by default, so you need to set EnableHostVerification to true if no Config is set.

```go
cluster := gocql.NewCluster("192.168.1.1", "192.168.1.2", "192.168.1.3")
cluster.SslOpts = &gocql.SslOptions{
	EnableHostVerification: true,
}
session, err := cluster.CreateSession()
if err != nil {
	return err
}
defer session.Close()
```

--------------------------------

### ExampleUDTUnmarshaler implementation

Source: https://pkg.go.dev/github.com/gocql/gocql

Full example of implementing a UDTUnmarshaler. It assumes a keyspace with a UDT and table as described in the comment. It queries a row and prints the unmarshaled fields, expecting 'a value' and '42'.

```go
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40
 * Copyright (c) 2016, The Gocql authors,
 * provided under the BSD-3-Clause License.
 * See the NOTICE file distributed with this work for additional information.
 */

package main

import (
	"context"
	"fmt"
	"log"

	gocql "github.com/gocql/gocql"
)

// MyUDTUnmarshaler implements UDTUnmarshaler.
type MyUDTUnmarshaler struct {
	fieldA string
	fieldB int32
}

// UnmarshalUDT unmarshals the field identified by name into MyUDTUnmarshaler.
func (m *MyUDTUnmarshaler) UnmarshalUDT(name string, info gocql.TypeInfo, data []byte) error {
	switch name {
	case "field_a":
		return gocql.Unmarshal(info, data, &m.fieldA)
	case "field_b":
		return gocql.Unmarshal(info, data, &m.fieldB)
	default:
		// If you want to be strict and return error un unknown field, you can do so here instead.
		// Returning nil will ignore unknown fields, which might be handy if you want
		// to be forward-compatible when a new field is added to the UDT.
		return nil
	}
}

// ExampleUDTUnmarshaler demonstrates how to implement a UDTUnmarshaler.
func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create type example.my_udt (field_a text, field_b int);
	create table example.my_udt_table(pk int, value frozen<my_udt>, PRIMARY KEY(pk));
	insert into example.my_udt_table (pk, value) values (1, {field_a: 'a value', field_b: 42});
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	var value MyUDTUnmarshaler
	err = session.Query("SELECT value FROM example.my_udt_table WHERE pk = 1").WithContext(ctx).Scan(&value)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(value.fieldA)
	fmt.Println(value.fieldB)
	// a value
	// 42
}
```

--------------------------------

### Iterating with MapScan using a new map each iteration

Source: https://pkg.go.dev/github.com/gocql/gocql

Example of using MapScan in a loop. A new map is created for each row, and the loop breaks when MapScan returns false. The example prints the 'fullname' field if present.

```go
iter := session.Query(`SELECT * FROM mytable`).Iter()
for {
	// New map each iteration
	row := make(map[string]interface{})
	if !iter.MapScan(row) {
		break
	}
	// Do things with row
	if fullname, ok := row["fullname"]; ok {
		fmt.Printf("Full Name: %s\n", fullname)
	}
}

```

--------------------------------

### func (c *Cache) Get(key string) (value interface{}, ok bool)

Source: https://pkg.go.dev/github.com/gocql/gocql/internal/lru

Get looks up a key's value from the cache.

```APIDOC
## func (c *Cache) Get(key string) (value interface{}, ok bool)

### Description
Get looks up a key's value from the cache.

### Parameters
- **key** (string) - The key to look up.

### Returns
- **value** (interface{}) - The value associated with the key, if present.
- **ok** (bool) - True if the key was found, false otherwise.
```

--------------------------------

### Implement Marshaler and Unmarshaler for custom version type

Source: https://pkg.go.dev/github.com/gocql/gocql

Complete Go program showing how to implement gocql.Marshaler and gocql.Unmarshaler for a custom type representing a version number stored as a string. It includes setup for a Cassandra cluster, inserting and selecting data, and demonstrates distinguishing between null and zero values.

```go
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/*
 * Content before git sha 34fdeebefcbf183ed7f916f931aa0586fdaa1b40
 * Copyright (c) 2016, The Gocql authors,
 * provided under the BSD-3-Clause License.
 * See the NOTICE file distributed with this work for additional information.
 */

package main

import (
	"context"
	"fmt"
	"log"
	"strconv"
	"strings"

	gocql "github.com/gocql/gocql"
)

// MyMarshaler implements Marshaler and Unmarshaler.
// It represents a version number stored as string.
type MyMarshaler struct {
	major, minor, patch int
}

func (m MyMarshaler) MarshalCQL(info gocql.TypeInfo) ([]byte, error) {
	return gocql.Marshal(info, fmt.Sprintf("%d.%d.%d", m.major, m.minor, m.patch))
}

func (m *MyMarshaler) UnmarshalCQL(info gocql.TypeInfo, data []byte) error {
	var s string
	err := gocql.Unmarshal(info, data, &s)
	if err != nil {
		return err
	}
	parts := strings.SplitN(s, ".", 3)
	if len(parts) != 3 {
		return fmt.Errorf("parse version %q: %d parts instead of 3", s, len(parts))
	}
	major, err := strconv.Atoi(parts[0])
	if err != nil {
		return fmt.Errorf("parse version %q major number: %v", s, err)
	}
	minor, err := strconv.Atoi(parts[1])
	if err != nil {
		return fmt.Errorf("parse version %q minor number: %v", s, err)
	}
	patch, err := strconv.Atoi(parts[2])
	if err != nil {
		return fmt.Errorf("parse version %q patch number: %v", s, err)
	}
	m.major = major
	m.minor = minor
	m.patch = patch
	return nil
}

// Example_marshalerUnmarshaler demonstrates how to implement a Marshaler and Unmarshaler.
func main() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create table example.my_marshaler_table(pk int, value text, PRIMARY KEY(pk));
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	value := MyMarshaler{
		major: 1,
		minor: 2,
		patch: 3,
	}
	err = session.Query("INSERT INTO example.my_marshaler_table (pk, value) VALUES (?, ?)",
		1, value).WithContext(ctx).Exec()
	if err != nil {
		log.Fatal(err)
	}
	var stringValue string
	err = session.Query("SELECT value FROM example.my_marshaler_table WHERE pk = 1").WithContext(ctx).
		Scan(&stringValue)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(stringValue)
	var unmarshaledValue MyMarshaler
	err = session.Query("SELECT value FROM example.my_marshaler_table WHERE pk = 1").WithContext(ctx).
		Scan(&unmarshaledValue)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(unmarshaledValue)
	// 1.2.3
	// {1 2 3}
}

```

--------------------------------

### Token-aware routing requires parameterized partition key

Source: https://pkg.go.dev/github.com/gocql/gocql

Shows that token-aware routing only works when all partition key columns are query parameters. The first example with a literal value is not token-aware; the second with parameters is.

```go
session.Query("select value from mytable where pk1 = 'abc' AND pk2 = ?", "def")
```

```go
session.Query("select value from mytable where pk1 = ? AND pk2 = ?", "abc", "def")
```

--------------------------------

### Use PasswordAuthenticator for username/password authentication

Source: https://pkg.go.dev/github.com/gocql/gocql

Set ClusterConfig.Authenticator to gocql.PasswordAuthenticator to use username/password authentication. The example shows creating a cluster, setting the authenticator, and creating a session.

```go
 cluster := gocql.NewCluster("192.168.1.1", "192.168.1.2", "192.168.1.3")
 cluster.Authenticator = gocql.PasswordAuthenticator{
		Username: "user",
		Password: "password"
 }
 session, err := cluster.CreateSession()
 if err != nil {
 	return err
 }
 defer session.Close()
```

--------------------------------

### Incorrect usage with 'use' statement

Source: https://pkg.go.dev/github.com/gocql/gocql

Example of incorrect usage: attempting to execute a 'use' statement after session creation. This will result in an error from the session.Query line.

```go
	cluster := gocql.NewCluster("192.168.1.1", "192.168.1.2", "192.168.1.3")
	cluster.Keyspace = "example"
	...
	session, err := cluster.CreateSession()

	if err = session.Query("use example2").Exec(); err != nil {
		log.Fatal(err)
	}
```

--------------------------------

### Iterating with MapScan using pointers in the map

Source: https://pkg.go.dev/github.com/gocql/gocql

Example of using MapScan with pointers to custom types and standard types. The map is populated with pointers before each call, and the loop breaks when MapScan returns false.

```go
var fullName FullName // Implements gocql.Unmarshaler and gocql.Marshaler interfaces
var address net.IP
var age int
iter := session.Query(`SELECT * FROM scan_map_table`).Iter()
for {
	// New map each iteration
	row := map[string]interface{}{
		"fullname": &fullName,
		"age":      &age,
		"address":  &address,
	}
	if !iter.MapScan(row) {
		break
	}
	fmt.Printf("First: %s Age: %d Address: %q\n", fullName.FirstName, age, address)
}

```

--------------------------------

### Customize cluster options (Keyspace, Consistency, ProtoVersion)

Source: https://pkg.go.dev/github.com/gocql/gocql

After creating a cluster configuration, you can customize options such as Keyspace, Consistency, and ProtoVersion. The driver tries to auto-detect the protocol version if not set, but setting it explicitly is recommended during cluster upgrades.

```go
cluster.Keyspace = "example"
cluster.Consistency = gocql.Quorum
cluster.ProtoVersion = 4
```
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