entity framework 5 MaxLength

Question

I was using EF4 and a piece of code I found to get the MaxLength value from an entity like this:

public static int? GetMaxLength(string entityTy         


        

Answer 1

I refactored mccow002's example into a copy-paste-ready Extension method class:

using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Metadata.Edm;

public static class DbContextExtensions
{

    // get MaxLength as an extension method to the DbContext
    public static int? GetMaxLength(this DbContext context, Expression> column)
    {
        return (int?)context.GetFacets(column)["MaxLength"].Value;
    }

    // get MaxLength as an extension method to the Facets (I think the extension belongs here)
    public static int? GetMaxLength(this ReadOnlyMetadataCollection facets)
    {
        return (int?)facets["MaxLength"].Value;            
    }

    // just for fun: get all the facet values as a Dictionary 
    public static Dictionary AsDictionary(this ReadOnlyMetadataCollection facets) {
        return facets.ToDictionary(o=>o.Name,o=>o.Value);
    }


    public static ReadOnlyMetadataCollection GetFacets(this DbContext context, Expression> column)
    {
        ReadOnlyMetadataCollection result = null;

        var entType = typeof(T);
        var columnName = ((MemberExpression)column.Body).Member.Name;

        var objectContext = ((IObjectContextAdapter)context).ObjectContext;
        var test = objectContext.MetadataWorkspace.GetItems(DataSpace.CSpace);

        if (test == null)
            return null;

        var q = test
            .Where(m => m.BuiltInTypeKind == BuiltInTypeKind.EntityType)
            .SelectMany(meta => ((EntityType)meta).Properties
            .Where(p => p.Name == columnName && p.TypeUsage.EdmType.Name == "String"));

        var queryResult = q.Where(p =>
        {
            var match = p.DeclaringType.Name == entType.Name;
            if (!match)
                match = entType.Name == p.DeclaringType.Name;

            return match;

        })
            .Select(sel => sel)
            .FirstOrDefault();

        result = queryResult.TypeUsage.Facets;

        return result;

    }

}