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   How to: Access Data in SQL Query Results
   How to: Bind an XPCollection to a LookUp
   How to: Bind an XPCollection to Standard Controls
   How to: Bind an XPCollection to the DataGrid
   How to: Bind an XPCollection to the Grid
   How to: Build Complex Criteria
   How to: Build Simple Criteria
   How to: Change Inheritance Mapping
   How to: Connect to a SQL Server
   How to: Connect to SQL Azure
   How to: Connect XPO to a Database Other than MS SQL or MS Access
   How to: Control Automatic Saving of Objects when Editing in a Grid
   How to: Create an Aggregated Object
   How to: Delay Property Loading
   How to: Filter By DateTime Values
   How to: Filter Persistent Objects by Type
   How to: Handle Persistent Object Initialization
   How to: Implement a Custom Criteria Language Function Operator
   How to: Implement a Full-Text Search
   How to: Implement Custom Functions and Criteria in LINQ to XPO
   How to: Implement Many-to-Many Relationships
   How to: Implement One-to-One Relationships
   How to: Link Classes Located in Different Assemblies
   How to: Make a Class or Property Non-Persistent
   How to: Make XPCollection Create Objects of Specific Type when They are Created via Bound Controls
   How to: Map to Custom Tables (Views) and Columns
   How to: Obtain a Collection of Persistent Objects by a Set of Their IDs
   How to: Obtain a Collection of Persistent Objects for Processing
   How to: Persist a BLOB Field
   How to: Prevent Changes in a Persistent Object from being Automatically Committed
   How to: Restore Deleted Objects
   How to: Use Pageable Collections
   How to: Use Read-Only Persistent Properties
   How to: Use the ContainsOperator for Objects in a Many-to-Many Relationship
   How to: Validate an Object
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How to: Filter Persistent Objects by Type

This topic describes how to filter persistent objects by their type.

Expanded ObjectType Field

To filter objects by type, you can use the ObjectType service field (see When and Why XPO Extends the Database Schema).

Expanded IsExactType and IsInstanceOfType Function Operators

Alternatively, you can use the IsExactType and IsInstanceOfType function operators (see Criteria Language Syntax).

Assume you have a collection of Employee objects. Employees can either be objects of the LocalEmployee or ForeignEmployee types:

The following code snippet demonstrates how the employees collection can be filtered to contain only foreign employees.

For details on the IsExactType and IsInstanceOfType operators, refer to the IsExactTypeFunction and IsInstanceOfTypeFunction class descriptions

Expanded Display the Object Type in UI

To display the type in UI, you can implement the following calculated property using the PersistentAliasAttribute:

Expanded See Also

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