Entity Framework Intercept Generate Migration Script - entity-framework

Question

I use Entity Framework 6.2 Code First (.net framework 4.6.1) and I map few entities to view via Table Attribute. It works for select operations and I handle Insert/Update/Delete with writing trigger to view at sql server side. It works as expected, however when I add a new migration, Entity Framework generate RenameTable scripts for used Table Attribute (actuallyis expected behavior for EF). But I want to intercept migration generation and change these entities tableName to original name.
my code like;
[MapToView("Users","UsersView")]
public class User
{
...
}
I wrote MapToView Attribute, this attribute inherited by TableAttribute and pass to second parameter to TableAttribute. I create this Attribute because if I intercept migration generation, return original table name with this attribute parameters.
In this case when I run "add-migration migrationName" it creates migration scripts like this;
RenameTable(name: "dbo.Users", newName: "UsersView");
but i want to create empty migration when I run "add-migration migrationName" script.
anyone can help me?

Answer 1

I solve the problem.
First: Problem is; When I Map Entity to View EF Code-first generate migration with ViewName. This is problem because I want to use View Instead of Table. So I solve problem with this instructions;
1- I Create BaseEntityConfiguration that Inherited from EntityTypeConfiguration and all entity configuration classes are inherited by.
for example:
public class UserConfig: BaseEntityConfiguration<User> //Generic Type is Entity
{
public UserConfig()
{
}
}
2- I Create MapToViewAttribute that inherited by TableAttribute
public class MapToViewAttribute : TableAttribute
{
public string TableName { get; }
public string ViewName { get; }
public MapToViewAttribute(string tableName, string viewName) : base(viewName)
{
TableName = tableName;
ViewName = viewName;
}
}
3- I Use MapToViewAttribute for example User Entity to use View.
[MapToView("User","UserView")]
public class User
{
...
}
And in BaseEntityConfiguration's Constructor I Get Generic Type and custom attributes. If any entity has MapToView Attribute, I pass to TableName parameter to ToTable Method. So at runtime EF uses View for these entities but doesn't create migration with RenameTable for these entities.
protected BaseEntityConfiguration()
{
var baseType = typeof(TEntityType);
var attributes = baseType.GetCustomAttributes(true);
foreach (var attr in attributes)
{
if (attr.GetType() == typeof(MapToViewAttribute))
{
var tableName = ((MapToViewAttribute)attr).TableName;
ToTable(tableName);
}
}
}
Last EF don't use your configuration files, so you must tell the EF to use this in DbContext class's InternalModelCreate method.
My implementation like this;
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
var typesToRegister = Assembly.GetExecutingAssembly()
.GetTypes().Where(IsConfigurationType);
foreach (var type in typesToRegister)
{
dynamic configurationInstance = type.BaseType != null
&& type.BaseType.IsGenericType
&& type.BaseType.GetGenericTypeDefinition() == typeof(BaseEntityConfiguration<>)
? Activator.CreateInstance(type, culture)
: Activator.CreateInstance(type);
modelBuilder.Configurations.Add(configurationInstance);
}
modelBuilder.Types().Configure(t => t.ToTable(t.ClrType.Name));
BaseDbContext.InternalModelCreate(modelBuilder);
}
But if you use this approach you must create Insert, Update and Delete Triggers/Rule (if you use SQLServer trigger is an option but if you use postgresql rule is better option) because EF uses this view for insert, update and delete operations.