Unique Key Error in Entity Framework Code First

Question

My Class

public class Dept_Master { [Key] public int Dept_Id { get; set; } [Index(IsUnique =true)] public string Dept_Name { get; set; } public bool status { get; set; } }

Error on Following

Server Error in '/' Application.

Column 'Dept_Name' in table 'dbo.Dept_Master' is of a type that is invalid for use as a key columnin an index.

Description: An unhandled exception occurred during the

execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Data.SqlClient.SqlException: Column 'Dept_Name' in table 'dbo.Dept_Master' is of a type that is invalid for use as a key column in an index.

I guess Dept_Name is (n)varchar(max) which makes it non eligible for unique constraint — jbl
– jbl, Commented Jun 14, 2016 at 7:37

Vignesh · Accepted Answer · 2016-06-14 09:09:15Z

When you use a VARCHAR(Max), we will get this error. Please try using:

[Column(TypeName = "VARCHAR")] [StringLength(n)] [Index(IsUnique = true)] public string Dept_Name { get; set; }

where n is between 1 and 450.

Vidhyadhar Galande · Accepted Answer · 2016-06-14 10:31:24Z

Two Way You can assign unique key

1) [Column(TypeName = "NVARCHAR")] [StringLength(2000)] [Index(IsUnique = true)] public string Dept_Name { get; set; } 2) [Column(TypeName = "VARCHAR")] [Index(IsUnique = true)] public string Dept_Name { get; set; }

@do not required for String length varchar datatype

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