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Referring back to table 17.6, you ll notice that no Insert, Update, or Delete methods were generated. Instead, those are called via SubmitChanges. SubmitChanges is an asynchronous batching operation. It handles sending all method calls to the server, with the exception of Invoke and Query operations. When you insert new items or delete existing items, those operations occur only on the client. When you call SubmitChanges, it loops through the entities on the client and sends to the server those entities that require a persistence operation, calling the appropriate operation for each entity. To cancel all pending changes for the domain context, call the RejectChanges method. It reverts entities back to their previous state, removes any newly inserted items, and reinstates any deleted items. The domain context is the client-side proxy for the domain service, as well as the container within which all instances of a given entity reside. It provides an interface for invoke operations and query operations, as well as an implicit interface to the insert, update, and delete operations through the SubmitChanges method. The entity classes Employee and Contact both inherit from a common client-side base class that provides much of the required change-tracking and other plumbing functionality. This class is named, appropriately enough, Entity.
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17.4.3 The Entity class
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Each client-side entity you work with, Employee and Contact in this example, derives from the Entity base class. This class provides a number of important change-tracking properties and methods. Table 17.7 shows the most important public members of the Entity base class Your derivations of the Entity class (the Contact class and the Employee class) also include all the individual properties that correspond to the fields coming from the database. Because this code was generated by the tools and not shared with the server, the properties have INotifyPropertyChanged and several other events injected into them. In this way, your otherwise-plain classes on the server can support binding and
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Table 17.7 Important public members of the Entity class Member Description
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EntityState HasChanges HasValidationErrors ValidationErrors GetOriginal
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The data state of this entity: Detached, Unmodified, Modified, New, or Deleted Indicates that this entity has changed since the last time it was saved Indicates that this entity has failed validation Returns a collection of validation errors Returns an instance of the unchanged entity from cache
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events on the client. To give you an idea of the robustness of the properties set up, listing 17.3 shows the Gender property for the Employee.
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Listing 17.3 The generated client-side Employee Entity property Gender
[DataMember()] [Required()] Validation [StringLength(1)] attributes public string Gender { get { return this._gender; } set { if ((this._gender != value)) { this.OnGenderChanging(value); this.RaiseDataMemberChanging("Gender"); this.ValidateProperty("Gender", value); this._gender = value; this.RaiseDataMemberChanged("Gender"); this.OnGenderChanged(); } } }
The setter for the property includes a number of calls to generated methods. Those methods perform validation and take care of INotifyPropertyChanged notification as well as raise information events, such as DataMemberChanging and DataMemberChanged. In this example, the OnGenderChanging and OnGenderChanged methods are partial methods that you can implement in a buddy class on the client, should you wish. A buddy class is a partial class you create to augment an existing partial class. In this way, you can modify the behavior of the class without introducing an inherited class. Note the use of attributes to tell the UI that this is a required field with a maximum length of 1. This information was automatically inferred from the entity model on the
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server at code-generation time. For that reason, changes to the database will require updates to the .edmx model and then automatic downstream updates here. In addition to the validation and display attributes described in chapters 12 and 13 and shown in this example, a number of other attributes are used in the entity. Although we ll get to how to use the special validation and display metadata attributes in the next section, table 17.8 shows some of the helper attributes you ll likely run across.
Table 17.8 Interesting attributes on the Employee Entity Description Indicates that this property should be serialized by WCF and is part of the data contract. Specifies that the property is part of a relationship, such as a foreign key. You ll find this on the nested entities such as Contact. Indicates that this property shouldn t be serialized. Useful on nested entities. Sends the object back to the server with its original value when the object is updated, even though this property hasn t changed. Indicates that this field is part of the primary key.
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