<!doctype html>
<html>
<head>
<meta charset="utf-8" />
<title>Minimal example of using Lovefield</title>
<script src="bower_components/lovefield/dist/lovefield.min.js"></script>
</head>
<body>
<script>
var schemaBuilder = lf.schema.create('todo', 1);
schemaBuilder.createTable('Item').
addColumn('id', lf.Type.INTEGER).
addColumn('description', lf.Type.STRING).
addColumn('deadline', lf.Type.DATE_TIME).
addColumn('done', lf.Type.BOOLEAN).
addPrimaryKey(['id']).
addIndex('idxDeadline', ['deadline'], false, lf.Order.DESC);
var todoDb;
var item;
schemaBuilder.connect().then(function(db) {
todoDb = db;
item = db.getSchema().table('Item');
var row = item.createRow({
'id': 1,
'description': 'Get a cup of coffee',
'deadline': new Date(),
'done': false
});
return db.insertOrReplace().into(item).values([row]).exec();
}).then(function() {
return todoDb.select().from(item).where(item.done.eq(false)).exec();
}).then(function(results) {
results.forEach(function(row) {
console.log(row['description'], 'before', row['deadline']);
});
});
</script>
</body>
</html>The example todo app above resides here. In order to run it locally, navigate to that folder in your checkout and follow the instructions below.
- Install gulp (if you have not already),
npm install -g gulp - Install bower (if you have not already),
npm install -g bower - Pull dependencies in package.json,
npm install . - Pull dependencies in bower.json,
bower install - Start a local webserver,
gulp debug - Navigate to http://localhost:8000/todo.html.
Besides downloading directly from GitHub repository, Lovefield supports npm
and bower package management systems and can be found using
npm info lovefield
bower info lovefieldAdding Lovefield as the dependency and executing npm update or bower update
will automatically pull down the designated release.
The concept of Lovefield is to define a database schema, then operate on the instance implementing that schema. In the example, schema definition is carried out through a set of synchronous APIs:
// SQL equivalent: CREATE DATABASE IF NOT EXISTS todo
// This schema definition (or data definition commands in SQL, DDL) is not
// executed immediately. Lovefield uses builder pattern to build the schema
// first, then performs necessary database open/creation later.
var schemaBuilder = lf.schema.create('todo', 1);
// SQL equivalent:
// CREATE TABLE IF NOT EXISTS Item (
// id AS INTEGER,
// description AS INTEGER,
// deadline as DATE_TIME,
// done as BOOLEAN,
// PRIMARY KEY ON ('id')
// );
// ALTER TABLE Item ADD INDEX idxDeadLine(Item.deadline DESC);
schemaBuilder.createTable('Item').
addColumn('id', lf.Type.INTEGER).
addColumn('description', lf.Type.STRING).
addColumn('deadline', lf.Type.DATE_TIME).
addColumn('done', lf.Type.BOOLEAN).
addPrimaryKey(['id']).
addIndex('idxDeadline', ['deadline'], false, lf.Order.DESC);The code above has pseudo SQL commands to demonstrate their equivalent concept in SQL. Once the schema is defined, Lovefield needs to be instructed to create or connect to the corresponding instance:
// Promise-based API to get the instance.
schemaBuilder.connect().then(function(db) {
// ...
});From this point on, the schema cannot be altered. Both the connect() and
Lovefield offered query APIs are asynchronous Promise-based APIs. This design
is to prevent Lovefield from blocking main thread since the queries can be
long running and demanding quite some CPU and I/O cycles.
If the database is brand new, Lovefield will create it using the schema. If the database already exists, Lovefield will attempt to identify the instance using database name specified in the schema, and connect to it.
Lovefield also uses Promise chaining pattern extensively:
// Start of the Promise chaining
schemaBuilder.connect().then(function(db) {
// Asynchronous call connect() returned object: db
todoDb = db;
// Get the schema representation of table Item.
// All schema-related APIs are synchronous.
item = db.getSchema().table('Item');
// Creates a row. Lovefield does not accept plain objects as row.
// Use the createRow() API provided in table schema to create a row.
var row = item.createRow({
'id': 1,
'description': 'Get a cup of coffee',
'deadline': new Date(),
'done': false
});
// INSERT OR REPLACE INTO Item VALUES row;
// The exec() method returns a Promise.
return db.insertOrReplace().into(item).values([row]).exec();
}).then(function() {
// When reached here, Lovefield guarantees previous INSERT OR REPLACE
// has been committed with its implicit transaction.
// SELECT * FROM Item WHERE Item.done = false;
// Return another Promise by calling this SELECT query's exec() method.
return todoDb.select().from(item).where(item.done.eq(false)).exec();
}).then(function(results) {
// The SELECT query's Promise will return array of rows selected.
// If there were no rows, the array will be empty.
results.forEach(function(row) {
// Use column name to directly dereference the columns from a row.
console.log(row['description'], 'before', row['deadline']);
});
});