Is it possible to retrieve connection string inside DDL generation template in VS2010?

I am playing around with creating a T4 template for the "DDL Generation Template option" (model first) process in Visual Studio 2010 RC. Is it possible to retrieve the connection string that is associated with that process? If I right click on the .edmx file and choose "Generate Database from Model..." I have the option of choosin开发者_运维知识库g a data connection. That connection string is saved to the app.config (assuming that the option is checked). So I am wondering if it is possible to retrieve that connection string inside the T4 template. I would like to generate different information from the template based on the connection string.

More generally, is it possible to get any context information in this situation? So far, the only thing I have successfully retrieved is the .NET data provider name.

Note - I have studied the ideas provided by Craig but am only getting the name of the IDE (devenv.exe), which quite possibly means I am just doing something wrong.

In case this helps anyone else, here is a snippet I created to read the Entity Framework connection string from inside T4. You pass it the model name (which is also the name of the connection string). It finds and parses just the connection bit I need. It also throws helpful errors when it does not succeed.

To use:

A. Paste this at the top of your template if you aren't already referencing these assemblies:

<#@ assembly name="EnvDTE" #>
<#@ assembly name="System.Configuration" #>

B. Paste this ugly (but compact) code at the end of your template:

<#+
string GetEFConnectionString(string modelName)
{
    string file = null, key = "provider connection string=\"";
    foreach (EnvDTE.ProjectItem item in ((EnvDTE.Project)((Array)((EnvDTE.DTE)((IServiceProvider)this.Host).GetService(typeof(EnvDTE.DTE))).ActiveSolutionProjects).GetValue(0)).ProjectItems)
        if (System.Text.RegularExpressions.Regex.IsMatch(item.Name, "(app|web).config", System.Text.RegularExpressions.RegexOptions.IgnoreCase)) {
            file = item.get_FileNames(0); break;
        }
    if (file == null) throw new Exception("config file could not be found");
    var config = System.Configuration.ConfigurationManager.OpenMappedExeConfiguration(new System.Configuration.ExeConfigurationFileMap() { ExeConfigFilename = file }, System.Configuration.ConfigurationUserLevel.None);
    var cn = config.ConnectionStrings.ConnectionStrings[modelName];
    if (cn == null) throw new Exception(modelName + " connection string could not be found");
    string s = cn.ConnectionString;    
    int pos = s.IndexOf(key,StringComparison.OrdinalIgnoreCase);    
    if (pos<0) throw new Exception("could not find value '" + key + "' inside connection string");
    pos += key.Length;
    int pos2=s.IndexOf('"',pos);
    if (pos2 < 0) throw new Exception("could not find ending \" in connection string");
    return s.Substring(pos,pos2-pos);
}
#>

C. Use it like such:

using(var connection = new SqlConnection(GetEFConnectionString("Database"))) {
    ..
}    

I posted my question on one of the MSDN forums and got a response from Lingzhi Sun who pointed me in the direction of a couple of links at skysanders.net. The second of these links has a very nice example of getting to the app/web.config file and, specifically the part I wanted, the connection strings. It doesn't give any information on the specific connection string for the scenario I described in the original question, but this gets me close enough.

• Accessing app.config/web.config from T4 template

• Accessing app.config/web.config from T4 template - Take 2

Well, the EF connection string will always have the same name as the model, right? The DB connection string will be embedded in the EF connection string. So I'd say you should be able to get it, at least indirectly, via the EF connection string.

Because you're not running in the assembly, have to specify the config file name.

So it would be something like:

var config = ConfigurationManager.OpenExeConfiguration(name);
var cs = config.ConnectoinStrings[modelName];

Note that name, here, is supposed to be an EXE name. But in the IDE, your config fine is going to be called App.config rather than MyApp.dll.config. So you may have to play around with this to get it to work -- try using "App" as the EXE name!

Worst case is open it as a file and then use the config manager.