实体框架生成了SQL查询

Question

I have an 2 EF entity defined as:

public class Event
{               
    public DateTime Created { get; set; }
    public string Id { get; set; }
    public bool Public { get; set; }
    public EventType Type { get; set; }

    public virtual ICollection<Note> Notes { get; set; }              
}

public class Note
{
    public string EventId { get; set; }      // Link to parent event
    public int Id { get; set; }
    public string Text { get; set; }

    public virtual Event Event { get; set; }
}

When accessing the Notes collection in Event , a SQL query is constructed in the form:

exec sp_executesql N'SELECT 
    [Extent1].[Id] AS [Id], 
    [Extent1].[EventId] AS [EventId], 
    [Extent1].[Text] AS [Text]
    FROM [dbo].[Notes] AS [Extent1]
    WHERE [Extent1].[EventId] = @EntityKeyValue1',
    N'@EntityKeyValue1 nvarchar(128)',
    @EntityKeyValue1=N'N5427961'

This query, given the data size and indexing used required in excess of 3000 reads. This seemed a bit much given the tables have sufficient indexing. Query analyser had no suggestions to speed the query up.

I then discovered if I changed the datatype being used in the SQL bind from nvarchar(128) to varchar(33) , which matches exactly the column type of EventId in the DB table, the query now only needed 8 reads.

Is this simply a case of me needing to use DataAnnotations to tell EF what the data types in SQL these fields are? or is something else happening here?

Answer 1

I found the way to most easily get the desired effect was:

modelBuilder.Entity<Event>().Property(x => x.Id).IsUnicode(false).HasMaxLength(33);

The other suggested method using annotation did not work and resulted in nvarchar still being used.