How do I set a column in SQL Server to varchar(max) using ASP.net EF Codefirst Data Annotations?

问题

I've been searching around the web trying to figure out the right syntax to have Entity Framework Code First create my table with a column: varchar(max).

This is what I have. By default this creates varchar(128). How do I create varchar(max)?

I have tried [MaxLength] without success.

Any help would be appreciated. Thanks!

[Column(TypeName = "varchar")]
public string MediaDesc { get; set; }

回答1:

[Column(TypeName = "varchar(MAX)")]

Surprisingly the most obvious solution works.

The [MaxLength] attribute only creates a varchar column with a max length that isn't MAX but - in my case (SQL Server Express 2008 R2) - 8000.

回答2:

This will get you nvarchar(max):

[StringLength(int.MaxValue)]

I don't think there's an attribute to force non-unicode (are you sure you want that?), so for varchar(max) you need a tweak in the DbContext:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Entity>().Property(x => x.MediaDesc).IsUnicode(false);
}

回答3:

Use [MaxLength] annotation.

[Column(TypeName = "varchar")]
[MaxLength]
public string MediaDesc { get; set; }

回答4:

[Column(TypeName = "varchar(MAX)")] results in varchar(Max) in the database. If you have a custom convention setting strings MaxLength to 100, modelBuilder .Properties<string>() .Configure(c => c.IsUnicode(false).HasMaxLength(100)); you need to include the MaxLength attribute [Column(TypeName = "varchar(MAX)"), MaxLength]. If you dont, you will get varchar(MAX) in the database but validation will throw for more that 100 characters

回答5:

Update for @Slauma answer.

Using a override for all strings like this in OnModelCreating:

modelBuilder.Properties<string>().Configure(s => 
    s.HasMaxLength(256).HasColumnType("nvarchar"));

and then modifying properties with attributes like this:

[Column(TypeName = "nvarchar(MAX)")]
public string CaseComment { get; set; }

Or this:

modelBuilder.Entity<YourClass>()
    .Property(b => b.CaseComment)
    .HasColumnType("nvarchar(MAX)");

This can cause the Exception. Validation failed for one or more entities. See 'EntityValidationErrors' property for more details. Even though the column is of correct data type Entity Framework still thinks it is nvarchar(256) and throws the error DbEntityValidationException.

To fix this use the following instead:

[Column(TypeName = "nvarchar(MAX)")]
[MaxLength]
public string CaseComment { get; set; }

modelBuilder.Entity<YourClass>()
    .Property(b => b.CaseComment)
    .HasColumnType("nvarchar(MAX)")
    .HasMaxLength(null);

来源：https://stackoverflow.com/questions/11235847/how-do-i-set-a-column-in-sql-server-to-varcharmax-using-asp-net-ef-codefirst-d

标签

sql-server

entity-framework

ef-code-first