Update LDL guide
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Raymond Feng
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docs/ldl.md
124
docs/ldl.md
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@ -4,7 +4,7 @@ LoopBack Definition Language (LDL) is simple DSL to define data models in JavaSc
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start with a model definition which describes the structure and types of data. The model establishes common knowledge of
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data in LoopBack.
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## Describing a model
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## Describing a simple model
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Let's start with a simple example in plain JSON.
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@ -88,44 +88,52 @@ That's it. Now you have a User constructor representing the user model.
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At this point, the constructor only has a set of accessors to model properties. No behaviors have been introduced yet.
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## Adding methods to a model constructor
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## Adding logic to a model
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Models describe the shape of data. To leverage the data, we'll add logic to the model for various purposes, such as:
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- Interact with the data store for CRUD
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- Add behavior around a model instance
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- Add service operations using the model as the context
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There are a few ways to add methods to a model constructor:
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1. Create the model constructor from a data source
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var DataSource = require('loopback-datasource-juggler').DataSource;
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var ds = new DataSource('memory');
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// Compile the user model definition into a JavaScript constructor
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var User = ds.define('User', UserDefinition);
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// Create a new instance of User
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User.create({id: 1, firstName: 'John', lastName: 'Smith'}, function(err, user) {
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console.log(user); // The newly created user instance
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User.findById(1, function(err, user) {
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console.log(user); // The user instance for id 1
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user.firstName = 'John1'; // Change the property
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user.save(function(err, user) {
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console.log(user); // The modified user instance for id 1
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});
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};
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});
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### 1) Create the model constructor from a data source
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A LoopBack data source injects methods on the model.
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2. Attach the model to a data source
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var DataSource = require('loopback-datasource-juggler').DataSource;
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var ds = new DataSource('memory');
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// Compile the user model definition into a JavaScript constructor
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var User = ds.define('User', UserDefinition);
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// Create a new instance of User
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User.create({id: 1, firstName: 'John', lastName: 'Smith'}, function(err, user) {
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console.log(user); // The newly created user instance
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User.findById(1, function(err, user) {
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console.log(user); // The user instance for id 1
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user.firstName = 'John1'; // Change the property
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user.save(function(err, user) {
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console.log(user); // The modified user instance for id 1
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});
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};
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});
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### 2) Attach the model to a data source
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A plain model constructor created from `ModelBuilder` can be attached a `DataSource`.
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var DataSource = require('loopback-datasource-juggler').DataSource;
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var ds = new DataSource('memory');
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User.attachTo(ds); // The CRUD methods will be mixed into the User constructor
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var DataSource = require('loopback-datasource-juggler').DataSource;
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var ds = new DataSource('memory');
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3. Manually declare methods to the model constructor
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User.attachTo(ds); // The CRUD methods will be mixed into the User constructor
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### 3) Manually declare methods to the model constructor
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We can add static and prototype methods to a model constructor.
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// Define a static method
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User.greet = function(msg) {
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console.log('Hello ', msg);
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@ -141,8 +149,42 @@ We can add static and prototype methods to a model constructor.
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console.log(user.getFullName()); // 'John Smith'
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## Exploring advanced features
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## Exploring advanced LDL features
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As we mentioned before, a complete model definition is an object with three properties:
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- name: The model name
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- options: An object of options, optional
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- properties: An object of property definitions
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### Model level options
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There are a set of options to control the model definition.
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- strict:
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- true: Only properties defined in the model are accepted. This is the default.
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- false: The model will be an open model. Unknown properties are accepted as well.
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- idInjection:
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- true: An `id` property will be added to the model automatically
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- false: No `id` property will be added to the model
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- Data source specific mappings
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The model can be decorated with connector-specific options to customize the mapping between the model and the connector.
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For example, we can define the corresponding schema/table names for Oracle as follows:
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{
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"name": "Location",
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"options": {
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"idInjection": false,
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"oracle": {
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"schema": "BLACKPOOL",
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"table": "LOCATION"
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}
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},
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...
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}
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### Property definitions
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The basic example use `propertyName: type` to describe a property.
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Properties can have options in addition to the type. LDL uses a JSON object to describe such properties, for example:
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@ -153,7 +195,7 @@ Properties can have options in addition to the type. LDL uses a JSON object to d
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Common options for a property are:
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### Data types
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#### Data types
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* type: The property type
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- String/Text
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@ -165,21 +207,15 @@ Common options for a property are:
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- Any/Object/JSON
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- GeoPoint
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#### Array types
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##### Array types
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LDL supports array types as follows:
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{emails: [String]}
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- `{emails: [String]}`
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- `{"emails": ["String"]}`
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- `{emails: [{type: String, length: 64}]}`
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or
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{"emails": ["String"]}
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or
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{emails: [{type: String, length: 64}]}
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#### Object types
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##### Object types
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A model often has properties that consist of other properties. For example, the user model can have an `address` property
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that in turn has properties such as `street`, `city`, `state`, and `zipCode`.
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@ -273,8 +309,7 @@ Oracle database table, you can use the following syntax:
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"oracle": {"column": "FIRST_NAME", "type": "VARCHAR", "length": 32}
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### Advanced example
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#### Advanced example
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var User = modelBuilder.define('User', {
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name: String,
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@ -296,13 +331,6 @@ Oracle database table, you can use the following syntax:
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friends: [String]
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});
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### Model level options
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LDL uses a list of options to control the definition of a model.
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- strict:
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- idInjection:
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- Data source specific mappings
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### Relations between models
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