{"id":37,"date":"2009-02-18T13:35:37","date_gmt":"2009-02-18T17:35:37","guid":{"rendered":"http:\/\/blogs.law.harvard.edu\/brandonhaynes\/?p=37"},"modified":"2009-02-18T13:41:58","modified_gmt":"2009-02-18T17:41:58","slug":"using-the-entity-framework-to-idatareader-adapter","status":"publish","type":"post","link":"https:\/\/archive.blogs.harvard.edu\/brandonhaynes\/2009\/02\/18\/using-the-entity-framework-to-idatareader-adapter\/","title":{"rendered":"Using the Entity Framework (LINQ to Entity) to IDataReader Adapter"},"content":{"rendered":"

In a recent article<\/a>, I developed a theoretical basis for an adapter that allows for the adaptation of Entity Framework (EF) entities into IDataReader-implementing form, and announced the preview availability<\/a> of this software.\u00a0<\/p>\n

Herein I describe with more specificity the use of the adapter generator and the resultant adapters, and announce the release of the first\u00a0production-ready version<\/a>\u00a0of the adapter generator software.<\/p>\n

<\/p>\n

To introduce the use of the IDataReaderAdapter generator, consider a\u00a0hypothetical\u00a0software package with a data-layer defined as:<\/p>\n

public interface IDataLayer
\n\u00a0\u00a0 \u00a0{
\n\u00a0\u00a0 \u00a0IDataReader GetSomeData();
\n\u00a0\u00a0 \u00a0IDataReader GetSomeOtherData(int aParameter);
\n\u00a0\u00a0 \u00a0}<\/code><\/div>\n

Business-process code interacts with this data logic exclusively through the IDataLayer interface; this not only creates a clean separation of concerns<\/a>, but also allows for run-time specification of arbitrary IDataLayer implementation (typically a la dependency injection<\/a>). \u00a0This might be concretely implemented as:<\/p>\n

public class DataLayer : IDataLayer
\n\u00a0\u00a0 \u00a0{
\n\u00a0\u00a0 \u00a0public IDataReader GetSomeData()
\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0{
\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0return SqlHelper.ExecuteReader(connectionString, \"GetSomeData\");
\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0}<\/code>
\n\u00a0\u00a0 \u00a0public IDataReader GetSomeOtherData(int aParameter)
\n\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0{
\n\u00a0\u00a0 \u00a0 \u00a0 \u00a0return SqlHelper.ExecuteReader(connectionString, \"GetSomeOtherData\", aParameter);
\n\u00a0\u00a0 \u00a0 \u00a0 \u00a0}
\n\u00a0\u00a0 \u00a0}<\/code><\/div>\n

For those developers wishing to move to Microsoft’s Entity Framework<\/a> (EF), this presents a problem. \u00a0There is no ready method by which one may convert an EntityObject<\/a>\u00a0into an IDataRecord (and, similarly, an IEnumerable<EntityObject> into IDataReader). \u00a0Without such a conversion, it is not possible to transition to the EF without breaking the IDataLayer interface contract. \u00a0For those applications that are widely deployed (or have strong third-party augmentation), this is a very real problem indeed.<\/p>\n

The IDataReaderAdapter generator allows for such a conversion in two ways:<\/p>\n

    \n
  1. Compile-time adaption an EF schema into a set of IDataRecord-implementing wrappers without<\/span> the use of reflection (and of O(n) property-lookup performance), or<\/li>\n
  2. Run-time adaption of an EntityObject (or any) object to an IDataRecord-implementing counterpart through the use of reflection.<\/li>\n<\/ol>\n
    Developers are free to choose the method of adaption based upon his or her particular needs.<\/div>\n

    Note:<\/strong>\u00a0The adapter generator may be used to adapt any<\/span>\u00a0objects into IDataRecord\/Reader-implementing objects. \u00a0Though the functionality described herein largely deals with the EF, the generator may be applied against any arbitrary object.<\/p>\n

    Method 1: Compile-Time Adaption of an Entity Framework Schema<\/h4>\n

    To produce IDataRecord\/Reader-implementing adapters at compile-time, we execute the adapter generator utility and point it at our EF schema. \u00a0The utility is executed in one of two ways, with syntax as:<\/p>\n

    IDataReaderAdapterGenerator
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0\/entities:[.NET Entity Framework EDMX file]
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0\/output:[output class filename]
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0[\/entities:[entity regex]
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0[\/language:vb|c#]<\/code><\/p>\n

    IDataReaderAdapterGenerator
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0\/assembly:
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0\/output:[output class filename]
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0[\/objects:[entity regex]
    \n\u00a0\u00a0 \u00a0 \u00a0 \u00a0[\/language:vb|c#]<\/code><\/p>\n