Pre-Generated Views With a Code First Model Entity Framework 6.0

By using the following code we can get a storage mapping collection.

var objectContext = ((IObjectContextAdapter)dbContext).ObjectContext;
var mappingCollection = (StorageMappingItemCollection)objectContext.MetadataWorkspace
    .GetItemCollection(DataSpace.CSSpace);

Once we have the Storage Mapping Item collection, we can access the methods of GenerateViews and ComputeMappingHashValue of the StorageMappingItemCollection class.

The GenerateViews method creates a dictionary of entities for each view in the container mapping and the ComputeMappingHashValue method computes the hash value for a single container mapping and it is very useful at runtime to identify whether there is no change in the model after generating views.

The DbMappingViewCache class has one property, MappingHashValue, and one method, GetView. MappingHashValue must return as generated by the ComputeMappingHashValue method. When the Entity Framework loads the view, it will first compare the hash value of the model and the hash returned by this property. If they do not match then the Entity Framework throws an exception type of EntityCommandCompilationException.

The GetView method accepts an EntitySetBase and returns a DbMappingVIew containing the Entity SQL that was generated for that that was associated with the given EntitySetBase in the dictionary generated by the GenerateViews method. The GetView method returns null when we do not have the required view.

public class MyMappingViewCache : DbMappingViewCache
{
    public override string MappingHashValue
    {
        get
        {
            return "df5a56995eb89ee1d0f7cd1c0bd989a32f6f6c500f524f64aba8f87706ab51ab";
        }
    }

    public override DbMappingView GetView(EntitySetBase extent)
    {
        if (extent == null)
        {
            throw new ArgumentNullException("extent");
        }

        var extentName = extent.EntityContainer.Name + "." + extent.Name;

        if (extentName == "CodeFirstDatabase.Employee")
        {
            return GetView0();
        }

        if (extentName == "Model.Employees")
        {
            return GetView1();
        }

        return null;
    }

    private static DbMappingView GetView0()
    {
        return new DbMappingView(@"
            SELECT VALUE --Constructing Employee [CodeFirstDatabaseSchema.Employee]
                T1.Employee_Id, T1.Employee_Code, T1.Employee_Name
            FROM
            (
                SELECT
                    T.Id AS Employee_Id,
                    T.Code AS Employee_Code,
                    T.Name AS Employee_Name,
                    True AS _from0
                FROM Model.Employees AS T
            ) AS T1");
    }

    private static DbMappingView GetView1()
    {
        return new DbMappingView(@"
            SELECT VALUE -- Constructing Employees [PreGeneratedView.Model.Employee]
                T1.Employee_Id, T1.Employee_Code, T1.Employee_Name
            FROM
            (
                SELECT
                    T.Id AS Employee_Id,
                    T.Code AS Employee_Code,
                    T.Name AS Employee_Name,
                    True AS _from0
                FROM CodeFirstDatabase.Employee AS T
            ) AS T1");
    }
}

Summary

Using the method described previously we can create a pre-generated view and using the pre-generated view we can improve the performance of the Entity Framework (first-time query execution).