Working with Data-Related Objects in Code

LightSwitch generates objects and members that describe your data. The names of these objects and members match the names of items in your solution. For example, if you add a table named Customer, LightSwitch generates an object named Customer. This topic describes each type of object that is generated by LightSwitch. To view code examples that use these objects and members to perform common data-related tasks, see Performing Data-Related Tasks by Using Code.

Hierarchy of Generated Objects and Members

The following illustration summarizes the generated objects and members of your data model.

Application

The Application object provides top level access to objects in your application. To access the Application object, open any user code file in the code editor, and then type Application. The types of methods and properties that appear in IntelliSense after you type Application and then type “.” will change based on the code file in which you are writing code. In most cases, you can use a property of the Application object to get an object that represents the current user.

Data Workspace

The DataWorkspace object is the top-level object for all data access. The DataWorkspace object contains a property for each data source in your project. For example, if you have a data source named NorthwindData, LightSwitch generates a property named NorthwinddData. When you type DataWorkspace in the Code Editor, the NorthwindData property becomes available in a drop-down list.

The following illustration shows some generated members that might appear in a drop-down list.

Data Source

LightSwitch generates an object for each data source in your project. This object contains members that you can use to access data. The members of a data source object include entity set properties and query methods.

The following illustration shows some generated members that might appear in a drop-down list.

Entity Set Properties

An entity set property returns a collection of entities. LightSwitch generates an entity set property for each entity in the data source. For example, if your data source contains an entity named Customer, LightSwitch generates a property named Customers. You could use the Customers property to get an EntitySet object that represents a collection of Customer entities.

The EntitySet object also contains members that enable you to check whether the current user has permission to read, update, or delete entities in the collection. For more information, see Performing Data-Related Tasks by Using Code.

Note

EntitySet is one of several types of entity collection objects. To optimize the performance of your code, make sure that you use the correct type of entity collection object for the type of business logic that you are writing. For more information, see Entity Collection Objects and Performance.

Query Methods

A query method gets the results of a query. LightSwitch generates a method for each query that is defined in your data source. The name of the method matches the name of the query. A query can return a single entity, or a collection of entities of type IDataServiceQueryable.

Note

IDataServiceQueryable<T> is one of several types of entity collection objects. To optimize the performance of your code, make sure that you use the correct type of entity collection object for the type of business logic that you are writing. For more information, see Entity Collection Objects and Performance.

By default, LightSwitch generates the following query methods for each entity in the data source.

1. <Entity Name>_Single.

2. <Entity Name>_SingleOrDefault.

Both of these methods accept a primary key segment and return a single entity object. If no entities are returned, the <Entity Name>_Single method throws an exception whereas the <Entity Name>_SingleOrDefault method returns a Null value (Nothing in Visual Basic).

Entities

LightSwitch generates an EntityObject for each entity in an entity collection. For example, if your code retrieved a collection of orders, the collection would contain an EntityObject that represents each order. An EntityObject contains members that you can use to delete an entity, read or update the value of entity properties, or get related entities. You can get an EntityObject from an entity collection object such as an EntitySet or by calling a query method that returns an entity. For more information, see Performing Data-Related Tasks by Using Code.

The following illustration shows the members of an Order entity named myOrder. The Order entity contains entity properties such as OrderDate, OrderID, and Freight. The Order entity also has members that you can use to get the related Order_Details collection and the Customer who placed the order.

In this example, the Customer property returns a Customer entity. A Customer entity is on the one side of the Customer-Order relationship.

The Order_Details property returns a collection of Order_Details entities. The Order_Details entity is on the many side of the Order-Order_Details relationship. The Order_Details collection object is of type EntityCollection.

This illustration also shows a property named Order_DetailsQuery. Properties that end in the with the word Query return an IDataServiceQueryable object.

Note

EntityCollection and IDataServiceQueryable are both types of entity collection objects. To optimize the performance of your code, make sure that you use the correct type of entity collection object for the type of business logic that you are writing. For more information, see Entity Collection Objects and Performance.

Entity Collection Objects and Performance

When you use an entity collection object in a LINQ expression, LightSwitch performs an operation that retrieves entities from the server tier. The type of object that you use determines whether LightSwitch retrieves all of the entities in a collection or only a subset of them. To ensure that your code performs as expected, choose the most appropriate type of collection object for the business logic that you are writing. There two types of entity collection objects: Objects that cause LightSwitch to evaluate a LINQ expression remotely, and objects that cause LightSwitch to evaluate a LINQ expression locally.

LINQ Operations: Remote vs. Local Execution

If you use an EntitySet or IDataServiceQueryable object in a LINQ expression, LightSwitch passes the entire LINQ expression to the data service of the server tier. Then, the results of the expression are passed back to the calling code. This type of query execution performs well because only entities that satisfy the query are returned to the calling code. However, only a subset of query operators is supported by the data service. If your expression requires other LINQ operators, consider using other types of collection objects.

The following illustration shows a LINQ expression that uses an IDataServiceQueryable object. This example shows the LINQ operation passing the entire expression to the data service and returning only Order entities that satisfy the conditions of the query.

If you use an EntityCollection or IEnumerable object in a LINQ expression, LightSwitch does not pass the expression to the data service. Instead, LightSwitch retrieves all entities of the given type. Then, the expression is applied to the entire collection locally. If an entity collection is large, this type of query execution can negatively affect performance. However, your code can use the full set of LINQ operators. In addition, this approach might make sense when you want to pass the full collection entities to other methods in your code.

The following illustration shows a LINQ expression that uses an EntityCollection object. This example shows the LINQ operation retrieving all Order entities for a particular customer. Then, the conditions of the query are applied to the entire collection locally.

Examples: Getting Entity Collection Objects in Code

The following shows how you can get collections of Order entities in the Northwind sample database.

To get this entity collection object	Use this code	Remote or Local Execution
EntitySet	DataWorkspace.Northwind.Orders or myOrder.Details.EntitySet()	Remote
IDataServiceQueryable	myCustomer.OrdersQuery or DataWorkspace.Northwind.Orders.GetQuery()	Remote
EntityCollection	myCustomer.Orders	Local
IEnumerable	myCustomer.OrdersQuery.Execute() or DataWorkspace.Northwind.Orders.GetQuery().Execute()	Local

See Also

Concepts

Performing Data-Related Tasks by Using Code

Writing Code in LightSwitch

Other Resources

Data: The Information Behind Your Application