How to Change Entity Framework Default Conventions, when Mapping Data ?

There are 3 ways.

1. Entity Framework Fluent API

2. Fluent Validation
       - Validation Library for .NET
       - This uses a fluent interface and lambda expressions for building validation rules
          for your business objects

3. Data Annotations 

          - Annotations only cover a subset of the Fluent Validation functionality

       

What is Entity Framework Fluent API ?

• When working with Entity Framework Code First the default behavior is to map your POCO classes to tables using a set of conventions baked into Entity Framework
• Sometimes, however you cannot or do not want to follow those conventions and need to map entities to something other than what the conventions dictate
• For such a scenario you can use Fluent API
• Can be Used Only with Code First Development
• This is used to define the mapping between your objects and the database

What Does Fluent API  do ?

• The Code First Fluent API is most commonly accessed by overriding the OnModelCreating method on your derived DbContext class

Which Tasks can be Achieved by using Fluent API ?

1. Property Mapping

2. Type Mapping

3. Configuring Relationships

On This Article I will explain Property Mapping with Fluent API.  

Articles Sample Code Here

1. Property Mapping

    - is used to configure attributes for each property belonging to an entity or complex type

    - is used to obtain a configuration object for a given property

    - the options on the configuration object are specific to the type being configured

                 e.g. IsUnicode is available only on string properties 

• How to Configure a Primary Key ?

          - The HasKey method is used to configure the InstructorID primary key on the

             OfficeAssignment type

       modelBuilder.Entity<OfficeAssignment>().HasKey(t => t.InstructorId);

• How to Configure a Composite Primary Key ?

         - DepartmentId and Name properties to be the composite primary key of the

           Department type

      modelBuilder.Entity<Department>()

           .HasKey(t => new { t.DepartmentId, t.Name });

• How to Switch off Identity for Numeric Primary Keys ?

         - DepartmentId property value will not be generated by the database

      modelBuilder.Entity<Department>()

          .Property(t => t.DepartmentId)

          .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

• How to Specify the Maximum Length on a Property ?

         - Name property should be no longer than 50 characters

         - If you make the value longer than 50 characters, you will get a 

            DbEntityValidationException exception

         - If Code First creates a database from this model it will also set the

            maximum length of the Name column to 50 characters 

      modelBuilder.Entity<Department>().Property(t => t.Name).HasMaxLength(50);

• How to Configure the Property to be Required ?

         - Name property is required

         - If you do not specify the Name, you will get a 

            DbEntityValidationException exception

         - If Code First creates a database from this model then the column used to store

            this property will be non-nullable

      modelBuilder.Entity<Department>().Property(t => t.Name).IsRequired(); 

• How to Specify Not to Map a CLR Property to a Column in the Database ?

      modelBuilder.Entity<Department>().Ignore(t => t.Budget);

• How to Map a CLR Property to a Specific Column in the Database ?

          - Maps the Name CLR property to the DepartmentName database column

       modelBuilder.Entity<Department>()

                .Property(t => t.Name)

                .HasColumnName("DepartmentName");

• How to Rename a Foreign Key That Is Not Defined in the Model ?

          - If you choose not to define a foreign key on a CLR type,

          - But want to specify what name it should have in the database

       modelBuilder.Entity<Course>()

          .HasRequired(c => c.Department)

          .WithMany(t => t.Courses)

          .Map(m => m.MapKey("ChangedDepartmentId"));

• How to Configure whether a String Property Supports Unicode Content ?

          - By default strings are Unicode (nvarchar in SQL Server)

          - You can use the IsUnicode method to specify that a string should be of varchar type

      modelBuilder.Entity<Department>().Property(t => t.Name).IsUnicode(false);

• How to Configure the Data Type of a Database Column ?

         - The HasColumnType method enables mapping to different representations

            of the same basic type

         - Using this method does not enable you to perform any conversion
            of the data at run time

         - Note that : IsUnicode is the preferred way of setting columns to varchar,

            as it is database agnostic

     modelBuilder.Entity<Department>()

                 .Property(p => p.Name)

                 .HasColumnType("varchar");

• How to Configure Properties on a Complex Type ?

         Way 1 : You can call Property on ComplexTypeConfiguration

       modelBuilder.ComplexType<Details>()

                   .Property(t => t.Location)

                   .HasMaxLength(20);

        Way 2 : You can also use the dot notation to access a property of a complex type

       modelBuilder.Entity<OnsiteCourse>()

            .Property(t => t.Details.Location)

            .HasMaxLength(20);

• How to Configure a Property to Be Used as an Optimistic Concurrency Token ?

       Way 1 : You can use either the ConcurrencyCheck attribute

                     or the IsConcurrencyToken method

      modelBuilder.Entity<OfficeAssignment>()

                  .Property(t => t.Timestamp)

                  .IsConcurrencyToken();

      Way 2 : You can also use the IsRowVersion method

     modelBuilder.Entity<OfficeAssignment>()

                 .Property(t => t.Timestamp)

                 .IsRowVersion();

Articles Sample Code Here

Conclusion

• You can use Fluent API with Code First development, when you want to override the default conventions maintained by the Entity Framework
• I will explain Type Mapping and Configuring Relationships with my future Blog Post
• So Try This and Enjoy it

I hope this helps to You.Comments and feedback greatly appreciated.

Happy Coding

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