Customizing the EF Entity Templates

The nice thing about Entity Framework is that anytime you are using one of the entity template generation capabilities, they are pretty easily customizable. This, of course, means that you are NOT using the pure code-first API most likely (however, to an existing database defines a T4 template). In this blog post, we’re going to quickly update the T4 template to change the default rendering:

using System;
using System.Collections.Generic;
    
public partial class State_LKP
{
    public int StateID { get; set; }
    public string StateCode { get; set; }
    public string StateName { get; set; }
}

To add additional information that the application can later use for metadata purposes, such as the following:

using System;
using System.Collections.Generic;
    
public partial class State_LKP
{
    public const string StateID_Name = "StateID";
    public int StateID { get; set; }
    
    public const int StateCode_MAX_LENGTH = 10;		
    public const string StateCode_Name = "StateCode";
    public string StateCode { get; set; }
    
    public const int StateName_MAX_LENGTH = 50;
    public const string StateName_Name = "StateName";
    public string StateName { get; set; }
}

Notice that each column has a constant defining the name, as well as a constant defining it’s max length defined in the database (if a string).

To do this, we need to open up the .tt file that generates each of the entities. In my version, around line 66, we have the following snippet.

var simpleProperties = typeMapper.GetSimpleProperties(entity);
if (simpleProperties.Any())
{
    foreach (var edmProperty in simpleProperties)
    {
#>
    <#=codeStringGenerator.Property(edmProperty)#>
<#
    }
}

Notice that this snippet loops through each of the simple properties (the properties defined one for each column) and renders out a definition (note codeStringGenerator is a class defined in the T4 template that defines all of the markup. I didn’t choose to modify that here). To add the name constants and the max length constants, the updated samples were changed to the following code sample. Comments below indicate the changes made.

var simpleProperties = typeMapper.GetSimpleProperties(entity);
if (simpleProperties.Any())
{
    //edmProperty of type EdmProperty
    foreach (var edmProperty in simpleProperties)
    {
        //Check max length - if any max length, then write out a constant
	 if(edmProperty.MaxLength.HasValue)
                {
                        #>
 
                        public const int <#= edmProperty.Name #>_MAX_LENGTH = 
                            <#= edmProperty.MaxLength.Value #>;
 
                        <#
                }	


         public const string <#= edmProperty.Name #>_Name = 
               "<#= edmProperty.Name #>";

    <#=codeStringGenerator.Property(edmProperty)#>
    <#
    }
}

Here we add constants to the output of the properties and everything generates great. You may say it would be better to use attributes; that is possible as well, but for that I’d recommend editing the CodeStringGenerator class (in the T4 template) and update the Property method directly instead.

The T4 template is available here: http://pastebin.com/42NiuwDE

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