How do I map a char property using the Entity Framework 4.1 “code only” fluent API?

问题

I have an object that has a char property:

public class Product
{
    public char Code
    {
        get;
        set;
    }
}

Entity Framework doesn't seem to be able to map chars (this field is missing from the database when I create the database schema from my model objects). Is there anyway I can map the char (e.g. to a string) using the fluent API? I don't want to change the model objects as they are part of a legacy shared library.

回答1:

Char is not valid primitive type for entity framework = entity framework doesn't map it. If you check CSDL reference you will see list of valid types (char is not among them).

Database char(1) is translated as string (SQL to CSDL translation). Char is described as non-unicode string with fixed length 1.

The only ugly option is second mapped property using string and your char non-mapped property will just use string[0] from that property. That is just another example how some simple type mapping or converters are damn missing in EF.

回答2:

In Fluent API you can specify the database column data type using the HasColumnType method like this:

modelBuilder.Entity<Product>()   
.Property(p => p.Code)   
.HasColumnType("char");

According to Andre Artus' answer here, HasColumnType is available in EF4.1.

For those using Data Annotations, the ColumnAttribute can accomplish the same thing.

[Column(TypeName="char")]
public string Code { get; set; }

回答3:

I have tried all the ways I have imagined and I must say the the accepted answer is the unique way to solve the problem of the char type as far as I know.

The char type isn't available for its use in EntityFramework.

Fluent API is included in this restriction.

If you try to put a char on the Property(p => p.MyCharProperty) will give you an Exception.

That means that char properties aren't available for Fluent API nor Attributes.

The easiest solution is this (as proposed by Ladislav Mrnka).

public class Product
{
    public char Code { get; set; }

    [Column("Code", TypeName="char")]
    [MaxLength(1)]
    public string CodeString
    {
         get { return Code.ToString(); }
         set { Code = value[0]; }
    }
}

One note: you can't put the property private, protected or internal. Must be public.

Fluent API version would be like this.

public class Product
{
    public char Code { get; set; }

    //We need the property but we will use the Fluent API to replace the attributes
    public string CodeString
    {
         get { return Code.ToString(); }
         set { Code = value[0]; }
    }
}

modelBuilder.Entity<Product>().Property(p => p.Code)
    .HasTypeName("char")
    .HasMaxLength(1)

回答4:

There is alternate ways to tackle this issue for TESTING purpose only. Make the field not null to null able for time being from design mode. Sometime it is restricted SQL Management Studio. (Change setting Tools -> Option ->Designer -> Table Database designer -> Uncheck "Prevent saving changes that required table creation"

来源：https://stackoverflow.com/questions/6760765/how-do-i-map-a-char-property-using-the-entity-framework-4-1-code-only-fluent-a

标签

entity-framework

char

ef4-code-only

fluent-interface