entity manager - Page 30

Opening an SQL CE file at runtime with Entity Framework 4

- by David Veeneman

I am getting started with Entity Framework 4, and I an creating a demo app as a learning exercise. The app is a simple documentation builder, and it uses a SQL CE store. Each documentation project has its own SQL CE data file, and the user opens one of these files to work on a project. The EDM is very simple. A documentation project is comprised of a list of subjects, each of which has a title, a description, and zero or more notes. So, my entities are Subject, which contains Title and Text properties, and Note, which has Title and Text properties. There is a one-to-many association from Subject to Note. I am trying to figure out how to open an SQL CE data file. A data file must match the schema of the SQL CE database created by EF4's Create Database Wizard, and I will implement a New File use case elsewhere in the app to implement that requirement. Right now, I am just trying to get an existing data file open in the app. I have reproduced my existing 'Open File' code below. I have set it up as a static service class called File Services. The code isn't working quite yet, but there is enough to show what I am trying to do. I am trying to hold the ObjectContext open for entity object updates, disposing it when the file is closed. So, here is my question: Am I on the right track? What do I need to change to make this code work with EF4? Is there an example of how to do this properly? Thanks for your help. My existing code: public static class FileServices { #region Private Fields // Member variables private static EntityConnection m_EntityConnection; private static ObjectContext m_ObjectContext; #endregion #region Service Methods /// <summary> /// Opens an SQL CE database file. /// </summary> /// <param name="filePath">The path to the SQL CE file to open.</param> /// <param name="viewModel">The main window view model.</param> public static void OpenSqlCeFile(string filePath, MainWindowViewModel viewModel) { // Configure an SQL CE connection string var sqlCeConnectionString = string.Format("Data Source={0}", filePath); // Configure an EDM connection string var builder = new EntityConnectionStringBuilder(); builder.Metadata = "res://*/EF4Model.csdl|res://*/EF4Model.ssdl|res://*/EF4Model.msl"; builder.Provider = "System.Data.SqlServerCe"; builder.ProviderConnectionString = sqlCeConnectionString; var entityConnectionString = builder.ToString(); // Connect to the model m_EntityConnection = new EntityConnection(entityConnectionString); m_EntityConnection.Open(); // Create an object context m_ObjectContext = new Model1Container(); // Get all Subject data IQueryable<Subject> subjects = from s in Subjects orderby s.Title select s; // Set view model data property viewModel.Subjects = new ObservableCollection<Subject>(subjects); } /// <summary> /// Closes an SQL CE database file. /// </summary> public static void CloseSqlCeFile() { m_EntityConnection.Close(); m_ObjectContext.Dispose(); } #endregion }

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