# IT:AD:EF/CodeFirst:HowTo:Define Models/Properties #



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## Examples: Properties ##

The following just specify contraints on size, key, etc.

 

#### Primary Key ####
It's done automatically if you the fieldname is called `Id` or `TheEntitityId`, but if you can't use that field name:

    modelBuilder.Entity<Manager>()
      .HasKey(ma => ma.ManagerCode);

#### Composite Keys ####
Use an anonymous object:

    modelBuilder.Entity<Department>()
      .HasKey(t => new { t.DepartmentID, t.Name });

#### MaxLength ####

    modelBuilder.Entity<Manager>().Property(ma => ma.Name)
      .HasMaxLength(20);

#### Required ####

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


#### Ignore ####
You can ignore calculated columns:

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


#### Mapping to a different Column ####

    modelBuilder.Entity<Department>().Property(t => t.Name)
      .HasColumnName("DepartmentName");



### CheckList: Class Properties ###

* MUST: mark Scalar Properties as `virtual` to enable improved Change Tracking (by going from Snapshot CT to Proxy POCO Change Tracking, which is based on `IPOCO`/`IEntityWithChangeTracker`).
* MUST: mark Collection Navigation Properties as `virtual` to enable lazy loading.
* MUST: Navigation Collection properties must implement `ICollection<Entities>`
* SHOULD: As we are working with proxies, can use `private set` for Id, etc:
    * `public string Id {get; private set;}`
* CONSIDER: For properties that need to ignored:
    * DataAnnotations: `[Ignore]` (see [[IT/AD/Code First/DataAnnotations/]]).
    * FluentAPI: within `DataContext.OnModelCreating()`: `modelBuilder.Entity<Department>().Ignore(t => t.Budget);` (see [[IT/AD/Code First/FluentAPI/Properties/]])
* CONSIDER: For derived calculated properties *that need to be saved*, use empty sets:
    * `public FullName {get {return _first + " " + _last;} set {}}`  
* CONSIDER: If you have to turn of Id autogeneration:
    * DataAnnotations: ? (see [[IT/AD/Code First/DataAnnotations/]])
    * FluentAPI: within `DataContext.OnModelCreating()`: `modelBuilder.Entity<Dept>().Property(t => t.ID).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);` (see [[IT/AD/Code First/FluentAPI/Properties/]])




#### Reference: Property Related FluentAPI ####

* [http://msdn.microsoft.com/en-us/library/hh295847(v=vs.103).aspx](http://msdn.microsoft.com/en-us/library/hh295847(v=vs.103).aspx)