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Golang cheatsheet

Materialize is wire-compatible with PostgreSQL, which means that Go applications can use the standard library’s database/sql package with a PostgreSQL driver to interact with Materialize. In this guide, we’ll use the pgx driver to connect to Materialize and issue SQL commands.

Connect

To connect to Materialize using pgx, you can use either a URI or DSN connection string:

package main

import (
	"context"
	"github.com/jackc/pgx/v4"
	"log"
)

func main() {

	ctx := context.Background()
	connStr := "postgres://MATERIALIZE_USERNAME:APP_SPECIFIC_PASSWORD@MATERIALIZE_HOST:6875/materialize"

	conn, err := pgx.Connect(ctx, connStr)
	if err != nil {
		log.Fatal(err)
	}
	defer conn.Close()
}

To create a concurrency-safe connection pool, import the pgxpool package and use pgxpool.Connect.

The remainder of this guide uses the *pgx.Conn connection handle from the connect section to interact with Materialize.

Create tables

Most data in Materialize will stream in via an external system, but a table can be helpful for supplementary data. For example, you can use a table to join slower-moving reference or lookup data with a stream.

To create a table named countries in Materialize:

createTableSQL := `
    CREATE TABLE IF NOT EXISTS countries (
        code CHAR(2),
        name TEXT
    );
`

_, err := conn.Exec(ctx, createTableSQL)
if err != nil {
    log.Fatal(err)
}

Insert data into tables

To insert a row of data into a table named countries in Materialize:

insertSQL := "INSERT INTO countries (code, name) VALUES ($1, $2)"

_, err := conn.Exec(ctx, insertSQL, "GH", "GHANA")
if err != nil {
    log.Fatal(err)
}

Query

Querying Materialize is identical to querying a PostgreSQL database: Go executes the query, and Materialize returns the state of the view, source, or table at that point in time.

Because Materialize maintains results incrementally updated, response times are much faster than traditional database queries, and polling (repeatedly querying) a view doesn’t impact performance.

To query the countries using a SELECT statement:

rows, err := conn.Query(ctx, "SELECT * FROM countries")
if err != nil {
    log.Fatal(err)
}

for rows.Next() {
    var r result
    err = rows.Scan(&r...)
    if err != nil {
        log.Fatal(err)
    }
    // operate on result
}

Manage sources, views, and indexes

Typically, you create sources, views, and indexes when deploying Materialize, but it’s possible to use a Go app to execute common DDL statements.

Create a source from Go

createSourceSQL := `
    CREATE SOURCE IF NOT EXISTS counter
    FROM LOAD GENERATOR COUNTER
    (TICK INTERVAL '500ms');
`

_, err = conn.Exec(ctx, createSourceSQL)
if err != nil {
    log.Fatal(err)
}

For more information, see CREATE SOURCE.

Create a view from Go

createViewSQL := `
    CREATE MATERIALIZED VIEW IF NOT EXISTS counter_sum AS
        SELECT sum(counter)
    FROM counter;
`

_, err = conn.Exec(ctx, createViewSQL)
if err != nil {
    log.Fatal(err)
}

For more information, see CREATE MATERIALIZED VIEW.

Stream

To take full advantage of incrementally updated materialized views from a Go application, instead of querying Materialize for the state of a view at a point in time, use a SUBSCRIBE statement to request a stream of updates as the view changes.

To read a stream of updates from an existing materialized view, open a long-lived transaction with BEGIN and use SUBSCRIBE with FETCH to repeatedly fetch all changes to the view since the last query:

tx, err := conn.Begin(ctx)
if err != nil {
    log.Fatal(err)
    return
}
defer tx.Rollback(ctx)

_, err = tx.Exec(ctx, "DECLARE c CURSOR FOR SUBSCRIBE counter_sum")
if err != nil {
    log.Fatal(err)
    return
}

for {
    rows, err := tx.Query(ctx, "FETCH ALL c")
    if err != nil {
        log.Fatal(err)
        tx.Rollback(ctx)
        return
    }

    for rows.Next() {
        var r subscribeResult
        if err := rows.Scan(&r.MzTimestamp, &r.MzDiff, ...); err != nil {
            log.Fatal(err)
        }
        fmt.Printf("%+v\n", r)
        // operate on subscribeResult
    }
}

err = tx.Commit(ctx)
if err != nil {
    log.Fatal(err)
}

The SUBSCRIBE output format of subscribeResult contains all of the columns of counter_sum, prepended with several additional columns that describe the nature of the update. When a row of a subscribed view is updated, two objects will show up in the result set:

{MzTimestamp:1646868332570 MzDiff:1 row...}
{MzTimestamp:1646868332570 MzDiff:-1 row...}

An MzDiff value of -1 indicates that Materialize is deleting one row with the included values. An update is just a retraction (MzDiff:-1) and an insertion (MzDiff:1) with the same timestamp.

Clean up

To clean up the sources, views, and tables that we created, first connect to Materialize using a PostgreSQL client and then, run the following commands:

DROP MATERIALIZED VIEW IF EXISTS counter_sum;
DROP SOURCE IF EXISTS counter;
DROP TABLE IF EXISTS countries;

Go ORMs

ORM frameworks like GORM tend to run complex introspection queries that may use configuration settings, system tables or features not yet implemented in Materialize. This means that even if a tool is compatible with PostgreSQL, it’s not guaranteed that the same integration will work out-of-the-box.

The level of support for these tools will improve as we extend the coverage of pg_catalog in Materialize and join efforts with each community to make the integrations Just Work™️.

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