Entity Framework provides several ways to intercept and customize the behavior of the framework during various stages of the database interaction process. These interception points allow developers to modify or enhance the behavior of the Entity Framework without modifying the core framework code.
The following are some of the interception points provided by Entity Framework:
- Query interception: This allows modifying or filtering the query results by intercepting the generated SQL queries.
- SaveChanges interception: Allows intercepting and modifying the changes made to entities before they are saved to the database.
- Change tracking interception: Allows intercepting and modifying changes made to entities before they are tracked by the change tracker.
- Validation interception: Allows intercepting and modifying the validation of entities before they are saved to the database.
To implement interception in Entity Framework, you can use the DbCommandInterceptor class, which provides a set of virtual methods to intercept various stages of the command execution process. You can create a custom interceptor by inheriting from this class and implementing the required methods. Here's an example of a custom interceptor that logs all the SQL queries executed by Entity Framework:
using System.Data.Common;
using System.Data.Entity.Infrastructure.Interception;
public class LoggingInterceptor : DbCommandInterceptor
{
public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
{
Console.WriteLine(command.CommandText);
base.ReaderExecuting(command, interceptionContext);
}
}
To register the interceptor with Entity Framework, you can add it to the DbInterception class as follows:
DbInterception.Add(new LoggingInterceptor());
This will intercept all SQL queries executed by Entity Framework and log them to the console. You can customize the behavior of the interceptor by modifying the implementation of the DbCommandInterceptor methods as required.
Let’s consider another example, a complex one. Let's say you have a database table Orders and you want to automatically set the OrderDate property to the current date when a new order is inserted. You can use interception to intercept the SaveChanges method and modify the entities before they are saved to the database.
First, you need to create an implementation of the IDbCommandInterceptor interface that intercepts the DbCommand that EF generates for inserting an order and sets the OrderDate property:
using System.Data.Common;
using System.Data.Entity.Infrastructure.Interception;
public class OrderInterceptor : IDbCommandInterceptor
{
public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
// Do nothing
}
public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
// Do nothing
}
public void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
{
// Do nothing
}
public void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
{
// Do nothing
}
public void ScalarExecuted(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
{
// Do nothing
}
public void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
{
// Do nothing
}
public void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
// Do nothing
}
public void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
{
// Check if the command is an insert command for the Orders table
if (command.CommandText.StartsWith("INSERT INTO [Orders]"))
{
// Get the current date and time
DateTime now = DateTime.Now;
// Add a parameter for the OrderDate column and set its value to the current date and time
DbParameter orderDateParam = command.CreateParameter();
orderDateParam.ParameterName = "@OrderDate";
orderDateParam.Value = now;
command.Parameters.Add(orderDateParam);
}
}
}
Next, you need to register the interceptor with Entity Framework in your DbContext class:
using System.Data.Entity;
public class MyDbContext : DbContext
{
public MyDbContext(string connectionString) : base(connectionString)
{
// Register the OrderInterceptor with Entity Framework
DbInterception.Add(new OrderInterceptor());
}
public DbSet<Order> Orders { get; set; }
}
Now, when you insert a new order into the Orders table using EF, the OrderDate property will automatically be set to the current date and time.
Category: Software
Tags: Dot Net C# Entity Framework