String Properties in ADO.NET Entity Data Model

(NOTE: This is Model First development in Entity Framework–start with a data model in the Entity Framework Designer and then generate database schema from the model).

When you add a scalar property of type string to an entity data model, you can fill in the values of several other properties within Visual Studio.

  • Fixed Length – (None), True, False
  • Max Length – (None), value, Max
  • Unicode – (None), True, False

stringprop

What does a value of (None) mean for these properties (when generating SQL Server Database from model)?

  • Fixed Length – (None) equivalent to False
  • Max Length – (None) equivalent to Max
  • Unicode – (None) equivalent to True

Here’s how choices for these properties map to SQL Server data types:

  • Fixed=True, Max=20 – nchar(20)
  • Fixed=(None), Max=20 – nvarchar(20)
  • Fixed=False, Max=20 – nvarchar(20)
  • Fixed=(None), Max=(None) – nvarchar(max)
  • Fixed=True, Max=(None) – nchar(4000)
  • Fixed=False, Max=(None) – nvarchar(max)
  • Fixed=(None), Max=Max – nvarchar(max)
  • Fixed=True, Max=Max – nchar(4000)
  • Fixed=False, Max=Max – nvarchar(max)
  • Fixed=(None), Max=20, Unicode=True – nvarchar(20)
  • Fixed=(None), Max=20, Unicode=False – varchar(20)

This means that if you just pick String as the type and set nothing else, you’ll get nvarchar(max) as the SQL Server type.

NOTE: The value of 4,000 is being used because the maximum length of a fixed length string in SQL Server is 4,000 characters (8,000 bytes when encoded as UTF-16).

 

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