Added Contstraint Based Expressions To Subsonic

comments edit

NUnit 2.4 introduces a really nice programming model they call Constraint-Based Assert Model. I believe MbUnit 2.4 will also have this. I really like this approach to building asserts because it reads almost like English.

Assert.That( myString, Is.EqualTo("Hello") );

Look at that fine piece of prose!

I’m so enamored of this approach I thought I’d try to bring it to Subsonic. Here is an example of two existing approaches to create a Query in Subsonic.

new Query("Products").WHERE("ProductId < 5");
new Query("Products").WHERE("ProductId", Comparison.LessThan, 5);

Now what don’t I like about these? Well in the first one, there’s no intellisence to guide me on making sure I choose a valid operator. Not only that, if that 5 is a variable instead, I’m doing some string concatenation, which I find to be ugly and harder to read such as this:

new Query("Products").WHERE("ProductId < " + productId);

The second one is much better in that I get the benefit of Intellisense and it is pretty readable and understandable. But can we do better? I mean, who talks like that? “Hand me the nails where the length is comparison greater than five.”

This is where I find the Constraint Based model to be very elegant and readable.

new Query("Products").WHERE("ProductId", Is.LessThan(5));

Now if you’re looking at this and wondering, where is the intellisense for the table name and column name? Don’t worry, it’s there. I used strings here for brevity. But here’s the final query with everything strongly typed.

new Query(Tables.Product, "Northwind")
  .WHERE(Product.Columns.ProductID, Is.LessThan(5))

This is just my first pass at this for Subsonic. I need to get a better understanding of how these queries are being built so I can add the following syntax next:

new Query("Products").WHERE("ProductId", Is.In(1,2,3,4,5);
// AND
new Query("Products").WHERE("ProductId", Is.In(new int[]{1,2,3,4});

This code has been committed to the trunk and is not yet in any release. It is pretty simple so far.

I wonder if I should propose the following syntax helper:

Select.From("Products").WHERE("ProductId", Is.LessThan(5));

//Where Select.From is defined as:

public static class Select
  public static Query From(string tableName)
    return new Query(tableName);

Or is that taking this too far. Thoughts?