better-sqlite3/docs/api.md

API

class Database

• new Database()
• Database#prepare() (see Statement)
• Database#transaction()
• Database#pragma()
• Database#checkpoint()
• Database#backup() (see Backup)
• Database#function()
• Database#aggregate()
• Database#loadExtension()
• Database#exec()
• Database#close()
• Properties

new Database(path, [options])

Creates a new database connection. If the database file does not exist, it is created. This happens synchronously, which means you can start executing queries right away.

Various options are accepted:

• options.memory: open an in-memory database, rather than a disk-bound one (default: false).

• options.readonly: open the database connection in readonly mode (default: false).

• options.fileMustExist: if the database does not exist, an Error will be thrown instead of creating a new file. This option does not affect in-memory or readonly database connections (default: false).

• options.timeout: the number of milliseconds to wait when executing queries on a locked database, before throwing a SQLITE_BUSY error (default: 5000).

const Database = require('better-sqlite3');
const db = new Database('foobar.db', { readonly: true });

.prepare(string) -> Statement

Creates a new prepared Statement from the given SQL string.

const stmt = db.prepare('SELECT name, age FROM cats');

.transaction(function) -> function

Creates a function that always runs inside a transaction. When the function is invoked, it will begin a new transaction. When the function returns, the transaction will be committed. If an exception is thrown, the transaction will be rolled back (and the exception will propagate as usual).

const insert = db.prepare('INSERT INTO cats (name, age) VALUES (@name, @age)');

const insertMany = db.transaction((cats) => {
  for (const cat of cats) insert.run(cat);
});

insertMany([
  { name: 'Joey', age: 2 },
  { name: 'Sally', age: 4 },
  { name: 'Junior', age: 1 },
]);

Transaction functions can be called from inside other transaction functions. When doing so, the inner transaction becomes a savepoint.

const newExpense = db.prepare('INSERT INTO expenses (note, dollars) VALUES (?, ?)');

const adopt = db.transaction((cats) => {
  newExpense('adoption fees', 20);
  insertMany(cats); // nested transaction
});

Transactions also come with deferred, immediate, and exclusive versions.

insertMany(cats); // uses "BEGIN"
insertMany.deferred(cats); // uses "BEGIN DEFERRED"
insertMany.immediate(cats); // uses "BEGIN IMMEDIATE"
insertMany.exclusive(cats); // uses "BEGIN EXCLUSIVE"

Caveats

If you'd like to manage transactions manually, you're free to do so with regular prepared statements (using BEGIN, COMMIT, etc.). However, manually managed transactions should not be mixed with transactions managed by this .transaction() method. In other words, using raw COMMIT or ROLLBACK statements inside a transaction function is not supported.

Transaction functions do not work with async functions. Technically speaking, async functions always return after the first await, which means the transaction will already be committed before any async code executes. Also, because SQLite3 serializes all transactions, it's generally a very bad idea to keep a transaction open across event loop ticks anyways.

It's important to know that SQLite3 may sometimes rollback a transaction without us asking it to. This can happen either because of an ON CONFLICT clause, the RAISE() trigger function, or certain errors such as SQLITE_FULL or SQLITE_BUSY. When this occurs, transaction functions will automatically detect the situation and handle it appropriately. However, if you catch one of these errors with a try-catch statement, you become responsible for handling the case. In other words, all catch statements within transaction functions should look like this:

try {
  ...
} catch (err) {
  if (!db.inTransaction) throw err; // (transaction was forcefully rolled back)
  ...
}

This situation generally only arises when checking for partial failures inside a nesting transaction.

.pragma(string, [options]) -> results

Executes the given PRAGMA and returns its result. By default, the return value will be an array of result rows. Each row is represented by an object whose keys correspond to column names.

Since most PRAGMA statements return a single value, the simple option is provided to make things easier. When simple is true, only the first column of the first row will be returned.

db.pragma('cache_size = 32000');
console.log(db.pragma('cache_size', { simple: true })); // => 32000

If execution of the PRAGMA fails, an Error is thrown.

It's better to use this method instead of normal prepared statements when executing PRAGMA, because this method normalizes some odd behavior that may otherwise be experienced. The documentation on SQLite3 PRAGMA can be found here.

.checkpoint([databaseName]) -> this

Runs a WAL mode checkpoint on all attached databases (including the main database).

Unlike automatic checkpoints, this method executes a checkpoint in "RESTART" mode, which ensures a complete checkpoint operation even if other processes are using the database at the same time. You only need to use this method if you are accessing the database from multiple processes at the same time.

setInterval(() => db.checkpoint(), 30000).unref();

If databaseName is provided, it should be the name of an attached database (or "main"). This causes only that database to be checkpointed.

If the checkpoint fails, an Error is thrown.

.backup(destination, [options]) -> Backup

Initiates a backup of the database, returning a new Backup object. You can optionally backup an attached database by setting the attached option to the name of the desired attached database.

If a backup cannot be started, an Error is thrown.

.function(name, [options], function) -> this

Registers a user-defined function so that it can be used by SQL statements.

db.function('add2', (a, b) => a + b);

db.prepare('SELECT add2(?, ?)').get(12, 4); // => 16
db.prepare('SELECT add2(?, ?)').get('foo', 'bar'); // => "foobar"
db.prepare('SELECT add2(?, ?, ?)').get(12, 4, 18); // => Error: wrong number of arguments

By default, user-defined functions have a strict number of arguments (determined by function.length). You can register multiple functions of the same name, each with a different number of arguments, causing SQLite3 to execute a different function depending on how many arguments were passed to it. If you register two functions with same name and the same number of arguments, the second registration will erase the first one.

If options.varargs is true, the registered function can accept any number of arguments.

If your function is deterministic, you can set options.deterministic to true, which may improve performance under some circumstances.

db.function('void', { deterministic: true, varargs: true }, () => {});

db.prepare("SELECT void()").get(); // => null
db.prepare("SELECT void(?, ?)").get(55, 19); // => null

.aggregate(name, options) -> this

Registers a user-defined aggregate function.

db.aggregate('addAll', {
  start: 0,
  step: (total, nextValue) => total + nextValue,
});

db.prepare('SELECT addAll(dollars) FROM expenses').pluck().get(); // => 92

The step() function will be invoked once for each row passed to the aggregate, using its return value as the new aggregate value. This works similarly to Array#reduce().

If options.start is a function, it will be invoked at the beginning of each aggregate, using its return value as the initial aggregate value. If options.start is not a function, it will be used as the initial aggregate value as-is (shown in the example above). If not provided, the initial aggregate value will be null.

You can also provide a result() function to transform the final aggregate value:

db.aggregate('getAverage', {
  start: () => [],
  step: (array, nextValue) => {
    array.push(nextValue);
  },
  result: array => array.reduce(sum) / array.length,
});

db.prepare('SELECT getAverage(dollars) FROM expenses').pluck().get(); // => 20.2

As shown above, you can use arbitrary JavaScript objects as your aggregation context, as long as a valid SQLite3 value is returned by result() in the end. If step() doesn't return anything (undefined), the aggregate value will not be replaced (be careful of this when using functions that return undefined when null is desired).

Just like regular user-defined functions, user-defined aggregates can accept multiple arguments. Furthermore, options.varargs and options.deterministic are also accepted.

If you provide an inverse() function, the aggregate can be used as a window function. Where step() is used to add a row to the current window, inverse() is used to remove a row from the current window. When using window functions, result() may be invoked multiple times.

db.aggregate('addAll', {
  start: 0,
  step: (total, nextValue) => total + nextValue,
  inverse: (total, droppedValue) => total - droppedValue,
  result: total => Math.round(total),
});

db.prepare(`
  SELECT timestamp, dollars, addAll(dollars) OVER day as dayTotal
  FROM expenses
  WINDOW day AS (PARTITION BY date(timestamp))
  ORDER BY timestamp
`).all();

.loadExtension(path) -> this

Loads a compiled SQLite3 extension and applies it to the current database connection.

It's your responsibility to make sure the extensions you load are compiled/linked against a version of SQLite3 that is compatible with better-sqlite3. Keep in mind that new versions of better-sqlite3 will periodically use newer versions of SQLite3. You can see which version is being used here.

db.loadExtension('./my-extensions/compress.so');

.exec(string) -> this

Executes the given SQL string. Unlike prepared statements, this can execute strings that contain multiple SQL statements. This function performs worse and is less safe than using prepared statements. You should only use this method when you need to execute SQL from an external source (usually a file). If an error occurs, execution stops and further statements are not executed. You must rollback changes manually.

const migration = fs.readFileSync('migrate-schema.sql', 'utf8');
db.exec(migration);

.close() -> this

Closes the database connection. After invoking this method, no statements can be created or executed.

process.on('exit', () => db.close());
process.on('SIGINT', () => db.close());
process.on('SIGHUP', () => db.close());
process.on('SIGTERM', () => db.close());

Properties

.open -> boolean - Whether the database connection is currently open.

.inTransaction -> boolean - Whether the database connection is currently in an open transaction.

.name -> string - The string that was used to open the database connection.

.memory -> boolean - Whether the database is an in-memory database.

.readonly -> boolean - Whether the database connection was created in readonly mode.

class Statement

An object representing a single SQL statement.

• Statement#run()
• Statement#get()
• Statement#all()
• Statement#iterate()
• Statement#pluck()
• Statement#expand()
• Statement#raw()
• Statement#columns()
• Statement#bind()
• Properties

.run([...bindParameters]) -> object

*(only on statements that do not return data)

Executes the prepared statement. When execution completes it returns an info object describing any changes made. The info object has two properties:

• info.changes: the total number of rows that were inserted, updated, or deleted by this operation. Changes made by foreign key actions or trigger programs do not count.
• info.lastInsertRowid: the rowid of the last row inserted into the database (ignoring those caused by trigger programs). If the current statement did not insert any rows into the database, this number should be completely ignored.

If execution of the statement fails, an Error is thrown.

You can specify bind parameters, which are only bound for the given execution.

const stmt = db.prepare('INSERT INTO cats (name, age) VALUES (?, ?)');
const info = stmt.run('Joey', 2);

console.log(info.changes); // => 1

.get([...bindParameters]) -> row

*(only on statements that return data)

Executes the prepared statement. When execution completes it returns an object that represents the first row retrieved by the query. The object's keys represent column names.

If the statement was successful but found no data, undefined is returned. If execution of the statement fails, an Error is thrown.

You can specify bind parameters, which are only bound for the given execution.

const stmt = db.prepare('SELECT age FROM cats WHERE name = ?');
const cat = stmt.get('Joey');

console.log(cat.age); // => 2

.all([...bindParameters]) -> array of rows

*(only on statements that return data)

Similar to .get(), but instead of only retrieving one row all matching rows will be retrieved. The return value is an array of row objects.

If no rows are found, the array will be empty. If execution of the statement fails, an Error is thrown.

You can specify bind parameters, which are only bound for the given execution.

const stmt = db.prepare('SELECT * FROM cats WHERE name = ?');
const cats = stmt.all('Joey');

console.log(cats.length); // => 1

.iterate([...bindParameters]) -> iterator

*(only on statements that return data)

Similar to .all(), but instead of returning every row together, an iterator is returned so you can retrieve the rows one by one. If you plan on retrieving every row anyways, .all() will perform slightly better.

If execution of the statement fails, an Error is thrown and the iterator is closed.

You can specify bind parameters, which are only bound for the given execution.

const stmt = db.prepare('SELECT * FROM cats');

for (const cat of stmt.iterate()) {
  if (cat.name === 'Joey') {
    console.log('found him!');
    break;
  }
}

.pluck([toggleState]) -> this

*(only on statements that return data)

Causes the prepared statement to only return the value of the first column of any rows that it retrieves, rather than the entire row object.

You can toggle this on/off as you please:

stmt.pluck(); // plucking ON
stmt.pluck(true); // plucking ON
stmt.pluck(false); // plucking OFF

When plucking is turned on, expansion and raw mode are turned off (they are mutually exclusive options).

.expand([toggleState]) -> this

*(only on statements that return data)

Causes the prepared statement to return data namespaced by table. Each key in a row object will be a table name, and each corresponding value will be a nested object that contains the associated column data. This is useful when performing a JOIN between two tables that have overlapping column names. If a result column is an expression or subquery, it will be available within the special $ namespace.

You can toggle this on/off as you please:

stmt.expand(); // expansion ON
stmt.expand(true); // expansion ON
stmt.expand(false); // expansion OFF

When expansion is turned on, plucking and raw mode are turned off (they are mutually exclusive options).

.raw([toggleState]) -> this

*(only on statements that return data)

Causes the prepared statement to return rows as arrays instead of objects. This is primarily used as a performance optimization when retrieving a very high number of rows. Column names can be recovered by using the .columns() method.

You can toggle this on/off as you please:

stmt.raw(); // raw mode ON
stmt.raw(true); // raw mode ON
stmt.raw(false); // raw mode OFF

When raw mode is turned on, plucking and expansion are turned off (they are mutually exclusive options).

.columns() -> array of objects

*(only on statements that return data)

This method is primarily used in conjunction with raw mode. It returns an array of objects, where each object describes a result column of the prepared statement. Each object has the following properties:

• .name: the name (or alias) of the result column.
• .column: the name of the originating table column, or null if it's an expression or subquery.
• .table: the name of the originating table, or null if it's an expression or subquery.
• .database: the name of the originating database, or null if it's an expression or subquery.
• .type: the name of the declared type, or null if it's an expression or subquery.

const fs = require('fs');

function* toRows(stmt) {
  yield stmt.columns().map(column => column.name);
  yield* stmt.raw().iterate();
}

function writeToCSV(filename, stmt) {
  return new Promise((resolve, reject) => {
    const stream = fs.createWriteStream(filename);
    for (const row of toRows(stmt)) {
      stream.write(row.join(',') + '\n');
    }
    stream.on('error', reject);
    stream.end(resolve);
  });
}

When a table's schema is altered, existing prepared statements might start returning different result columns. However, such changes will not be reflected by this method until the prepared statement is re-executed. For this reason, it's perhaps better to invoke .columns() after .get(), .all(), or .iterate().

.bind([...bindParameters]) -> this

Binds the given parameters to the statement permanently. Unlike binding parameters upon execution, these parameters will stay bound to the prepared statement for its entire life.

After a statement's parameters are bound this way, you may no longer provide it with execution-specific (temporary) bound parameters.

This method is primarily used as a performance optimization when you need to execute the same prepared statement many times with the same bound parameters.

const stmt = db.prepare('SELECT * FROM cats WHERE name = ?').bind('Joey');
const cat = stmt.get();

console.log(cat.name); // => "Joey"

Properties

.database -> object - The parent database object.

.source -> string - The source string that was used to create the prepared statement.

.reader -> boolean - Whether the prepared statement returns data.

class Backup

An object that facilitates a backup of the database.

• Backup#transfer()
• Backup#abort()
• Properties

.transfer([pageCount]) -> object

Transfers the specified number of database pages to the backup file. If a pageCount is not provided, all remaining pages are transferred. After the pages are transferred, it returns an object with the following properties:

• .totalPages: the total number of pages in the source database (and thus, the number of pages that the backup will have when completed) at the time of this transfer operation.
• .remainingPages: the number of pages that still must be transferred before the backup is complete.

It's important to understand that because the database can be modified between transfer operations, the returned object only provides an estimate of the backup progress. Also, if the source database is busy (being used by another process simultaneously), it's possible for this method to return without actually transferring any pages, regardless of the desired pageCount (an error will not be thrown).

If a fatal error occurs, an Error is thrown and the backup operation is automatically aborted.

Each transfer is a blocking operation, but you can access the database in a normal way between transfers. The example below demonstrates how you could perform a backup asynchronously, configuring exactly how much thread time is allotted to the backup operation.

const PAGES_PER_TRANSFER = 100;
const THREAD_UTILIZATION = 0.1; // This means 10%

const sleep = ms => new Promise(done => setTimeout(done, ms));

async function backupAsync(db, destination) {
  const backup = db.backup(destination);
  let time, ms, carryover = 0;

  while (true) {
    // Execute a transfer, and measure its duration.
    time = process.hrtime();
    backup.transfer(PAGES_PER_TRANSFER);
    if (backup.state === 'completed') break;
    time = process.hrtime(time);
    ms = time[0] * 1e3 + time[1] / 1e6;

    // Sleep for a while, and measure the actual sleep duration.
    const sleepTarget = ms / THREAD_UTILIZATION - ms + carryover;
    time = process.hrtime();
    await sleep(Math.max(0, Math.round(sleepTarget)));
    time = process.hrtime(time);
    ms = time[0] * 1e3 + time[1] / 1e6;

    // Keep track of the imprecision (don't trust setTimeout).
    carryover = sleepTarget - ms;
  }
}

In the future, it may be possible to use better-sqlite3 within a worker thread. Currently though, worker threads do not support native addons.

.abort() -> this

Aborts the backup operation. If the backup was started on an existing database file, that database will be rolled back to its prior state. If the backup operation had created a new database file, that file will be left as an empty database.

backup.abort();

When a database connection is closed, any pending associated backups will automatically be aborted.

Properties

.database -> object - The source database object.

.filename -> string - The destination of the backup.

.state -> string - Either "pending", "completed", or "aborted".

Binding Parameters

This section refers to anywhere in the documentation that specifies the optional argument [...bindParameters].

There are many ways to bind parameters to a prepared statement. The simplest way is with anonymous parameters:

const stmt = db.prepare('INSERT INTO people VALUES (?, ?, ?)');

// The following are equivalent.
stmt.run('John', 'Smith', 45);
stmt.run(['John', 'Smith', 45]);
stmt.run(['John'], ['Smith', 45]);

You can also use named parameters. SQLite3 provides 3 different syntaxes for named parameters (@foo, :foo, and $foo), all of which are supported by better-sqlite3.

// The following are equivalent.
const stmt = db.prepare('INSERT INTO people VALUES (@firstName, @lastName, @age)');
const stmt = db.prepare('INSERT INTO people VALUES (:firstName, :lastName, :age)');
const stmt = db.prepare('INSERT INTO people VALUES ($firstName, $lastName, $age)');
const stmt = db.prepare('INSERT INTO people VALUES (@firstName, :lastName, $age)');

stmt.run({
  firstName: 'John',
  lastName: 'Smith',
  age: 45
});

Below is an example of mixing anonymous parameters with named parameters.

const stmt = db.prepare('INSERT INTO people VALUES (@name, @name, ?)');
stmt.run(45, { name: 'Henry' });