实体框架和配置。 从静态上下文调用

Question

I started wanting to generate code using T4. To do this I need data from database. Since all data within the project is already retrieved using EF, I choose to use EF. So within my project I created a utility class with a static method that returns the object I need. I found out, that running in the context of the T4 custom tool I cannot read from config. So I manually set the connectionstring of my context and it worked!

    private static string GetConnectionString()
    {
        //How to read from the web.config when running a T4 template ?
        //ConnectionStringSettings settings = ConfigurationManager.ConnectionStrings["XXXXXXX"];
        //var connectionString = settings.ConnectionString;
        var connectionString = @"Data Source=XXXXXX;Initial Catalog=XXXXXX;Integrated Security=SSPI;MultipleActiveResultSets=true;";
        return connectionString;
    }

Later on I added a project to my solution. Project A holds the class with the static method that returns an object. Now from code in Project B I wish to call that static method.

When running that code I get an error: " No Entity Framework provider found for the ADO.NET provider with invariant name 'System.Data.SqlClient'. Make sure the provider is registered in the 'entityFramework' section of the application config file. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information. "

When I install nuget package EF for project B , the code runs as expected. But this beats the whole purpose of creating a utility class in project A . The calling party should just receive the object regardless of its own context.

How can I fix this? How can I configure a static method to use EF and make it available for usage as a reference to calling parties, not knowing EF?

I think the answer will probably be something like overriding EF behaviour to read from the static context provided in the utility class instead of the configuration provided by current runtime. But how can you do this?

Answer 1

If you don't want to add the whole EF package then just add a reference to EntityFramework.SqlServer.dll in Project B.

Even though Project B references Project A it will not copy this file over because it is referenced in the config file in the EF Section.

 <entityFramework>
     <defaultConnectionFactory type="System.Data.Entity.Infrastructure.LocalDbConnectionFactory,    EntityFramework">
        <parameters>
           <parameter value="mssqllocaldb" />
        </parameters>
     </defaultConnectionFactory>
    <providers>
      <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
     </providers>
  </entityFramework>

See the providers section above, this tells entity framework where to find the provider your are using (System.Data.SqlClient)

Answer 2

The first part regarding the T4 template, I was able to resolve by setting the connectionstring manually:

    /// <summary>
    /// When calling from a T4 template, it seems you cannot use the ConfigurationManager.
    /// </summary>
    /// <returns></returns>
    private static string GetConnectionString()
    {
        var connectionString = string.Empty;

        if (ConfigurationManager.ConnectionStrings["DBContext"] != null)
        {
            connectionString = ConfigurationManager.ConnectionStrings["DBContext"].ConnectionString;
        }
        else if (System.Reflection.Assembly.GetExecutingAssembly().GetName().Name == "MyApplication")
        {
            ExeConfigurationFileMap configToUse = null;
            var possibleConfig = System.Reflection.Assembly.GetExecutingAssembly().Location + ".config";
            if (File.Exists(possibleConfig))
            {
                configToUse = new ExeConfigurationFileMap();
                configToUse.ExeConfigFilename = possibleConfig;
                var config = ConfigurationManager.OpenMappedExeConfiguration(configToUse, ConfigurationUserLevel.None);
                connectionString = config.ConnectionStrings.ConnectionStrings["DBContext"].ConnectionString;
            }
        }            
        return connectionString;
    }

I create a System.Data.Entity.DbContext using that connectionstring and feed it to the GenericUnitOfWork. Now the T4 is able to run my getData method properly.

When I call the getData method from another project I provide the connectionstring as a parameter. But still the getData method will only run properly if the calling assembly knows EntityFramework as a reference.

So I added a reference to EF in the other project. And it works.

But I am still not satisfied: how to configure my getData method that the calling assembly does not need to have a reference to EF? I mean that should be possible right?