EntityConnection & Metadata in EntityFramework

EntityConnection (System.Data.EntityClient.EntityConnection) is the class which provides an abstraction for the connection established by the framework.What exactly we mean by connection established by the framework? A ORM framework stands in between an object model and a data source so it needs to connect to both i.e the model and the data source.

When we add an Entity Data Model (*.edmx) a default connection string gets added to the solution as shown below:

As indicated in the figure above the two critical components, one is metadata (model) and another is provider (datasource). The datasource part is quite obvious and easy to understand so let’s concentrate on the metadata part of it.

The entity data model (*.edmx) contains three xml based sections:

• Storage Model define in Storage Schema Definition Language (SSDL)
• Conceptual Model (Class Model) defined in Conceptual Schema Definition Language(CSDL)
• Mapping defined in Mapping Specification Language(MSL)

By default settings, when the code is compiled these three xml blocks get embedded into the assembly as resources. So in the metadata connection string we need to specify name of the SSDL/MSDL/CSDL and from which assembly we need to download them. This is shown in the figure below:

If we can change the Metadata location to output directory as shown below then SSDL/MSDL/CSDL files will be separately generated in the output (bin) folder

The files will be be generated as shown below:

The connection string gets modified as shown below:

So far so good. Though in most of the cases it seems to me that embedding inside the assembly makes much more sense but some of the configuration crazy crowd might think otherwise as well.So how we can manipulate this programmatically through the API.It’s time to go back to the EntityConnection class.

The EntityConnection class has a constructor which accepts a connection string as shown above containing both database and metadata information.But in case there are many metadata files this will be extremely cumbersome & long.

So to do similar stuff using API we need to see metadata information is exposed through classes.

EntityConnection holds a reference to System.Data.Common.DbConnection & System.Data.Metadata.Edm.MetadataWorkspace as shown in the figure below

MetadataWorkspace is the class representing the metadata and it has the following constructor which accepts list of paths and assemblies.

• public MetadataWorkspace(IEnumerable<string> paths,IEnumerable<Assembly> assembliesToConsider)

The following code block shows how we can use this constructor to read the metadata from file system: Here I have passed null in the second parameter as we are not extracting metadata from assembly here.

This leads to the following ArgumentNullException exception.

{“Value cannot be null.\r\nParameter name: assembliesToConsider”}

However passing a empty list works

static void Main(string[] args)
        {
            DbConnection dbc = new SqlConnection(@"data source=.\SQLEXPRESS;initial catalog=AdventureWorksLT2008;
                                                integrated security=True;multipleactiveresultsets=True;");

            MetadataWorkspace mdw = new MetadataWorkspace(new List<String>()
                                                                {
                                                                    @"D:\Demos\EFSample\AdventureWorks.Sales\bin\Debug\SalesModel.csdl",
                                                                    @"D:\Demos\EFSample\AdventureWorks.Sales\bin\Debug\SalesModel.ssdl",
                                                                    @"D:\Demos\EFSample\AdventureWorks.Sales\bin\Debug\SalesModel.msl"
                                                                }
                                                                ,new List<Assembly>());
            AdventureWorksLT2008Entities a = null;

            try
            {
                a = new AdventureWorksLT2008Entities(new EntityConnection(mdw, dbc));
                Console.WriteLine(a.ProductCategories.First().Name);
            }
            finally
            {
                (a as IDisposable).Dispose();
            }
           
            Console.Read();
        }

Advertisements

Entity Framework CTP 4.0 – Many To Many Mappings

In my last post I had discussed about entity relationships,navigational properties and how we can fetch data from database into the entities.In this post we will examine the many to many relationships and how this can be modeled using POCO and the CTP 4.0 Code First Approach.We will consider three tables Person,Club and ClubMember where each Person can belong to multiple Clubs as shown below:

Entity Framework CTP 4.0 – Data Fetching

In the last two posts I have discussed about Entity Framework CTP 4.0 Code First Approach and Database Initialization.Now we will take a look at how to define relationships and navigational properties between the Entities and how data fetching is impacted by these.

Entity Framework CTP 4.0 – Database Initialization

In the last post we discussed about the basic steps involved in working with the new Entity Framework CTP 4.0 Code First Approach.Now we will take a look at each of these steps in a bit more detail.We will start with database initialization.

Entity Framework CTP 4.0 – Code First Approach

It has been a month or two  that Entity Framework CTP 4.0 bits have released.I had read through the feature list back then but could not manage time to take a detailed look until this weekend.I always felt that Entity Framework’s approach towards handling of configuration(object relational mappings) and plain .NET objects was bit restrictive and cumbersome respectively.The mappings are needed to be stored in Entity Data Model(.edmx) files which are nothing but xml files with object to relational store mapping information.There was no proper way to express this mapping through code or attributes.But with code first approach we will able to describe our model using plain .NET objects and map it to the database objects through .NET code.In this post we will discuss the very basic steps involved in doing so.

Entity Framework & Concurrency

ADO.NET Entity Framework is the Object Relational Mapping(ORM) framework from Microsoft which enables us to map .NET classes to objects(tables,views,stored procedures..etc) in a relational database.While studying any ORM framework it’s important to know about, how it handles concurrency and ensures data consistency.In this post we will look into what options ADO.NET Entity Framework provides for ensuring this consistency.

CASE Statement Equivalent in LINQ

Last Friday while having a discussion on various LINQ standard query operators the topic of expressing T-SQL CASE statement in LINQ came up.