sqlite package - crawshaw.io/sqlite - Go Packages

Overview ¶

Package sqlite provides a Go interface to SQLite 3.

The semantics of this package are deliberately close to the SQLite3 C API, so it is helpful to be familiar with http://www.sqlite.org/c3ref/intro.html.

An SQLite connection is represented by a *sqlite.Conn. Connections cannot be used concurrently. A typical Go program will create a pool of connections (using Open to create a *sqlitex.Pool) so goroutines can borrow a connection while they need to talk to the database.

This package assumes SQLite will be used concurrently by the process through several connections, so the build options for SQLite enable multi-threading and the shared cache: https://www.sqlite.org/sharedcache.html

The implementation automatically handles shared cache locking, see the documentation on Stmt.Step for details.

The optional SQLite3 compiled in are: FTS5, RTree, JSON1, Session, GeoPoly

This is not a database/sql driver.

Statement Caching ¶

Statements are prepared with the Prepare and PrepareTransient methods. When using Prepare, statements are keyed inside a connection by the original query string used to create them. This means long-running high-performance code paths can write:

stmt, err := conn.Prepare("SELECT ...")

After all the connections in a pool have been warmed up by passing through one of these Prepare calls, subsequent calls are simply a map lookup that returns an existing statement.

Streaming Blobs ¶

The sqlite package supports the SQLite incremental I/O interface for streaming blob data into and out of the the database without loading the entire blob into a single []byte. (This is important when working either with very large blobs, or more commonly, a large number of moderate-sized blobs concurrently.)

To write a blob, first use an INSERT statement to set the size of the blob and assign a rowid:

"INSERT INTO blobs (myblob) VALUES (?);"

Use BindZeroBlob or SetZeroBlob to set the size of myblob. Then you can open the blob with:

b, err := conn.OpenBlob("", "blobs", "myblob", conn.LastInsertRowID(), true)

Deadlines and Cancellation ¶

Every connection can have a done channel associated with it using the SetInterrupt method. This is typically the channel returned by a context.Context Done method.

For example, a timeout can be associated with a connection session:

ctx := context.WithTimeout(context.Background(), 100*time.Millisecond)
conn.SetInterrupt(ctx.Done())

As database connections are long-lived, the SetInterrupt method can be called multiple times to reset the associated lifetime.

When using pools, the shorthand for associating a context with a connection is:

conn := dbpool.Get(ctx)
if conn == nil {
	// ... handle error
}
defer dbpool.Put(c)

Transactions ¶

SQLite transactions have to be managed manually with this package by directly calling BEGIN / COMMIT / ROLLBACK or SAVEPOINT / RELEASE/ ROLLBACK. The sqlitex has a Savepoint function that helps automate this.

A typical HTTP Handler ¶

Using a Pool to execute SQL in a concurrent HTTP handler.

var dbpool *sqlitex.Pool

func main() {
	var err error
	dbpool, err = sqlitex.Open("file:memory:?mode=memory", 0, 10)
	if err != nil {
		log.Fatal(err)
	}
	http.HandleFunc("/", handle)
	log.Fatal(http.ListenAndServe(":8080", nil))
}

func handle(w http.ResponseWriter, r *http.Request) {
	conn := dbpool.Get(r.Context())
	if conn == nil {
		return
	}
	defer dbpool.Put(conn)
	stmt := conn.Prep("SELECT foo FROM footable WHERE id = $id;")
	stmt.SetText("$id", "_user_id_")
	for {
		if hasRow, err := stmt.Step(); err != nil {
			// ... handle error
		} else if !hasRow {
			break
		}
		foo := stmt.GetText("foo")
		// ... use foo
	}
}

For helper functions that make some kinds of statements easier to write see the sqlitex package.

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