My goal is to create a custom Attribute
and allow. Add-Migration
to have custom code generated based on it.
The Model and Attribute
class
public class MyAttribute: Attribute {}
public class MyModel
{
public int Id { get; set; }
[MyAttribute]
public string Name { get; set; }
}
The MigrationProvider
and AnnotationProvider
:
internal class MyMigrationsAnnotationProvider : SqliteMigrationsAnnotationProvider
{
public override IEnumerable<IAnnotation> For( IProperty property )
{
MemberInfo MInfo = property.PropertyInfo ?? ( MemberInfo ) property.FieldInfo;
MyAttribute MyAttr = MInfo?.GetCustomAttribute<MyAttribute>();
if ( MyAttr != null )
{
return base.For( property ).Concat( new IAnnotation[] { new Annotation( "MyAttribute", true ) } );
}
return base.For( property );
}
}
internal class MyMigrationsSqlGenerator : SqliteMigrationsSqlGenerator
{
public MyMigrationsSqlGenerator( IRelationalCommandBuilderFactory IRFactory, ISqlGenerationHelper ISHelper, IRelationalTypeMapper Mapper, IRelationalAnnotationProvider AnProvider )
: base( IRFactory, ISHelper, Mapper, AnProvider ) {}
protected override void Generate( AddColumnOperation operation, IModel model, MigrationCommandListBuilder builder )
{
throw new Exception( "Hello world" );
// Here's where I got it wrong.
// I thought I should be able to read the "MyAttribute" annotation from here and generate extra code in the Up method
/*
if( operation.FindAnnotation( "MyAttribute" ) != null )
{
builder.AppendLine( "Hello there, not sure if this would work." );
}
*/
}
}
class MyContext : DbContext
{
public DbSet<MyModel> MModel { get; set; }
protected override void OnConfiguring( DbContextOptionsBuilder optionsBuilder )
{
optionsBuilder.UseSqlite( "Data Source=mydata.db" );
optionsBuilder.ReplaceService<IMigrationsSqlGenerator, MyMigrationsSqlGenerator>();
optionsBuilder.ReplaceService<IMigrationsAnnotationProvider, MyMigrationsAnnotationProvider>();
}
}
Generated Migration codes ( with some clean up )
protected override void Up(MigrationBuilder migrationBuilder)
{
migrationBuilder.CreateTable(
name: "MyModel",
columns: table => new
{
Id = table.Column<string>(nullable: false),
Name = table.Column<string>(nullable: false)
.Annotation("MyAttribute", true),
});
// The following line is what I want it to be generated
migrationBuilder.Sql( "I WANT MY CUSTOM QUERY BE GENERATED HERE" );
}
protected override void Down(MigrationBuilder migrationBuilder)
{
migrationBuilder.DropTable( name: "MyModel" );
// The following line is what I want it to be generated
migrationBuilder.Sql( "I WANT MY CUSTOM QUERY BE GENERATED HERE" );
}
As you can see the MyAttribute
annotation is successfully added to the Up
method. However, I couldn't seem to override the Generate
method since there's no Hello world
exception throw while running Add-Migration
.
I am using EF Core 1.1.5
Thanks in advance!
The IMigrationsSqlGenerator
can only process a MigrationOperation
that has been generated. To detect changes in your new Attribute
, you will probably need to replace the IMigrationsModelDiffer
service. Then you can return a new SqlOperation (or custom type) with the other differences between the two models.
On the plus side, this means that you can generate undo operations in the Down process too.