This package provides a Node.js API for DuckDB. The API for this client is somewhat compliant to the SQLite Node.js client for easier transition.
For TypeScript wrappers, see the duckdb-async project.
Initializing
Load the package and create a database object:
const duckdb = require('duckdb');
const db = new duckdb.Database(':memory:'); // or a file name for a persistent DB
All options as described on Database configuration can be (optionally) supplied to the Database constructor as second argument. The third argument can be optionally supplied to get feedback on the given options.
const db = new duckdb.Database(':memory:', {
"access_mode": "READ_WRITE",
"max_memory": "512MB",
"threads": "4"
}, (err) => {
if (err) {
console.error(err);
}
});
Running a Query
The following code snippet runs a simple query using the Database.all() method.
db.all('SELECT 42 AS fortytwo', function(err, res) {
if (err) {
console.warn(err);
return;
}
console.log(res[0].fortytwo)
});
Other available methods are each, where the callback is invoked for each row, run to execute a single statement without results and exec, which can execute several SQL commands at once but also does not return results. All those commands can work with prepared statements, taking the values for the parameters as additional arguments. For example like so:
db.all('SELECT ?::INTEGER AS fortytwo, ?::STRING AS hello', 42, 'Hello, World', function(err, res) {
if (err) {
console.warn(err);
return;
}
console.log(res[0].fortytwo)
console.log(res[0].hello)
});
Connections
A database can have multiple Connections, those are created using db.connect().
const con = db.connect();
You can create multiple connections, each with their own transaction context.
Connection objects also contain shorthands to directly call run(), all() and each() with parameters and callbacks, respectively, for example:
con.all('SELECT 42 AS fortytwo', function(err, res) {
if (err) {
console.warn(err);
return;
}
console.log(res[0].fortytwo)
});
Prepared Statements
From connections, you can create prepared statements (and only that) using con.prepare():
const stmt = con.prepare('SELECT ?::INTEGER AS fortytwo');
To execute this statement, you can call for example all() on the stmt object:
stmt.all(42, function(err, res) {
if (err) {
console.warn(err);
} else {
console.log(res[0].fortytwo)
}
});
You can also execute the prepared statement multiple times. This is for example useful to fill a table with data:
con.run('CREATE TABLE a (i INTEGER)');
const stmt = con.prepare('INSERT INTO a VALUES (?)');
for (let i = 0; i < 10; i++) {
stmt.run(i);
}
stmt.finalize();
con.all('SELECT * FROM a', function(err, res) {
if (err) {
console.warn(err);
} else {
console.log(res)
}
});
prepare() can also take a callback which gets the prepared statement as an argument:
const stmt = con.prepare('SELECT ?::INTEGER AS fortytwo', function(err, stmt) {
stmt.all(42, function(err, res) {
if (err) {
console.warn(err);
} else {
console.log(res[0].fortytwo)
}
});
});
Inserting Data via Arrow
Apache Arrow can be used to insert data into DuckDB without making a copy:
const arrow = require('apache-arrow');
const db = new duckdb.Database(':memory:');
const jsonData = [
{"userId":1,"id":1,"title":"delectus aut autem","completed":false},
{"userId":1,"id":2,"title":"quis ut nam facilis et officia qui","completed":false}
];
// note; doesn't work on Windows yet
db.exec(`INSTALL arrow; LOAD arrow;`, (err) => {
if (err) {
console.warn(err);
return;
}
const arrowTable = arrow.tableFromJSON(jsonData);
db.register_buffer("jsonDataTable", [arrow.tableToIPC(arrowTable)], true, (err, res) => {
if (err) {
console.warn(err);
return;
}
// `SELECT * FROM jsonDataTable` would return the entries in `jsonData`
});
});
Loading Unsigned Extensions
To load unsigned extensions, instantiate the database as follows:
db = new duckdb.Database(':memory:', {"allow_unsigned_extensions": "true"});