How can I "warm up" a LinqToSql precompiled query?

Question

In LinqToSql, precompiled queries are great - but it still requires me to take the compilation performance hit the first time the query is used.

I would like to 'warm up' these precompiled queries in the background when the application starts up. Obviously I can do that by calling them with some default parameters - however this results in a needless hit to the database.

Is there any way to 'warm up' the precompiled query without calling out to the database?

I have taken a look at the CompliedQuery source code but it seems many of the classes needed are sealed and/or internal...

Answer 1

Ok, so looking at source code for the CompiledQuery which gets returned from CompiledQuery.Compile() we can verify that the query is only actually compiled once you invoke the method for the first time:

    ICompiledQuery compiled; 
    private object ExecuteQuery(DataContext context, object[] args) {
        if (context == null) { 
            throw Error.ArgumentNull("context");
        } 
        if (this.compiled == null) { 
            lock (this) {
                if (this.compiled == null) { 
                    // This is where the query is copmiled
                    this.compiled = context.Provider.Compile(this.query);
                    this.mappingSource = context.Mapping.MappingSource;
                }
            } 
        }
        // this is where the query is executed against the data store
        return this.compiled.Execute(context.Provider, args).ReturnValue;
    }

So there is no way to force the compilation without actually executing it.

However, I did find a hacky workaround for it which gives me what I need. There is a way we can execute the query thus causing the query to be precompiled without allowing the call to the database:

// compiled query
static Func<NorthwindDataContext, int, IQueryable<Order>> GetOrderById =
    CompiledQuery.Compile((NorthwindDataContext db, int orderId) => LINQ GOES HERE );


static void Warmup() 
{
    var context = new NorthwindDataContext("ConnectionString");
    // dispose the connection to force the attempted database call to fail
    context.Connecction.Dispose(); 
    try  
    {
         GetOrderById(context, 1);
    }
    catch (Exception ex)
    {
         // we expect to find InvalidOperationException with the message
         // "The ConnectionString property has not been initialized."
         // but the underlying query will now be compiled
    }
}

static void GetData() 
{
     // as long as we called warmup first, this will not take the compilation performance hit
     var context = new NorthwindDataContext("ConnectionString");
     var result = GetOrderById(context, 1);
}