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This article mainly shows you the "Entity Framework 7 shadow attributes how to use", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "Entity Framework 7 shadow attributes how to use" this article.

Shadow properties are fields that do not exist in the class itself, but Entity Framework thinks they exist. They can participate in queries, create / update operations, and database migrations. Microsoft believes that there are two main application scenarios for shadow properties:

Allow the data access layer to access properties that should not be exposed by the domain model to other parts of the application

Allows developers to efficiently add attributes to classes without source code

The shadow property is defined in the OnModelCreating event, which is an overloaded method in DBContext. Here is an example of binding the DataTime attribute LastUpdated to a Blog entity.

Protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () .Property ("LastUpdated");

A common use case for this property is to automatically assign a value to the LastUpdated property when the save operation is performed. To do this, you can use DBContext.ChangeTracker to get a list of objects of type DBEntry. You can write like this:

Foreach (var item in modifiedEntries) {Item.Property ("LastModified") .CurrentValue = DateTime.Now;}

This can generally be achieved by overloading the SaveChanges () method of the DBContext class. With the overload here, you can update all the data that needs to be updated without having to repeat the code in every place where the data is updated.

When ChangeTracker is suitable for modifying and saving events, you will want to bypass DBEntry and access shadow properties directly. You can do this through the EF.Property function, as follows:

EF.Property (entity, "LastModified")

This expression is placed in a query to generate server-side WHERE and ORDER BY clauses.

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