LINQ Query Pane in VistaDB 4.1

There is a new pane in the Data Builder for VistaDB 4.1.  The LINQ query pane is a very handy way to build and test LINQ queries against a simple Entity Framework model.  First understand that this pane is a work in progress.  It was designed to be an easy way to write LINQ queries (similar to LINQPad) for your VistaDB database.  The feature is of limited usefulness since the model cannot be customized at generation, or loaded from your own assembly.  But this is where we were with the feature when we had to ship, so here it is.  We have been using it a lot to help write LINQ queries, we hope you find it useful too.

The current implementation only supports C# (sorry VB guys, it was on the list).  You can right click on the Entity Model tree and Script the main query window with all your basic CRUD operations.

By default the dialog is grayed out until you generate a model.  The code shown will still be present once the model is generated.

Generate a Model

By default the dialog is grayed out until you generate a model.  The code shown will still be present once the model is generated.

Click the Generate Model button to have Data Builder call the EDMGEN tool and build a default model for the current database.  The default is to output one type per table.  This is the same as if you add a new model to your application and accept all the defaults.  If any errors occur during the generation of the model they will be output in the Log window at the bottom of the screen.

When to generate a model

Each time Data Builder loads you will have to regenerate a new model (they are not saved across application runs).  The models are kept loaded after the initial generation.  If you make schema or foreign key changes you should regenerate the model in order for the changes to be present in the model.

How to view the current model

The current model is displayed on the second tab (after a model has been generated).

Intellisense

Sorry, there is no intellisense in the current version for the LINQ queries.  It REALLY does help to have it, but there just was not time to get it implemented.  Use the Entity Model tab to see what the entity names look like.

Right Click for Scripting

Right clicking on an entity (the table name) will allow you to generate some default LINQ queries for the Query pane.

Each of the basic CRUD operations are demonstrated for the object.  Selecting them will put the script in the query window.

Putting queries into your code

Once you have a query working the way you want, you can copy and paste it into your code.  The only requirements are that you have a model that matches the default model, and that you have a data context of your model called context (or you can rename the internal context to be what your variable is named).

A best practice for this code might look something like this:

using( RealModel.ModelEntities context = new RealModel.ModelEntities(connection))
{
   var query = from i in context.OrderDetails select new { i.OrderID, i.Orders.OrderDate };
   // Your custom code to work with the LINQ results
}

Example LINQ Queries

The example script code will not all execute by default.  They are templates for you to edit.  For example the delete template doesn’t know what your criteria is for the delete.  It leaves a string in the place for you to change to your actual criteria.

The idea was to eventually give the user an interactive wizard type of experience to build up their LINQ queries against the model.  But what is there today is still useful.

Summary

The LINQ panel in Data Builder 4.1 is a very useful way to write LINQ queries against a default EF model quickly with VistaDB.  It is not feature complete, but is still useful enough for us to release it with this version.

We hope you find it useful for writing LINQ queries, and possibly to interest you enough to learn more about Entity Framework.