Zeeshan Hirani

I have seen this misunderstanding starting to popup more often on how to delete an entity from a related collection. Suppose we have the following entity data model where a Person has many Phones identified by 1-to-many association as shown.

When you import a database view using Entity Data Model wizard,you will get an entity that has the same number of columns and data type as the view does.Suppose I have the following view in my database.

Last week i discovered a feature of Entity Data Model which i have not seen extensively being promoted. I accidentally run into it because of the size of my model. If you have a large model and want to search for an entity, it becomes tedious to zoom in and out and scroll up and down to find your entity. In Entity Framework 4, on the model browser there is a new search option that allows you to search for any artifact on your model, whether it be a property, association, column, entity. Below are some ways to search for any artifact on the model.

LINQ has a really cool operator call Let that lets you declare variables inside the query. The benefit i find in using let is, it makes my query much easier to read because using Let keyword i can create a variable and assign it a calculated value. Then later in my query i can test my value against that variable. In LINQ to entities if you are using let keyword, you want to be aware of how the sql is generated. There are cases where let keyword introduces extra or repetitive joins that are un-needed. Let’s see an example of where let introduces extra join when the linq query is translated. In the figure below I have a SalesRep entity that has an optional 0..1 association with RepSalesStatus. RepSalesStatus table in the database contains the totalsales a given rep has done. Since the association is optional there could be reps in our database that have not done any sales as yet.

Well the title of my post is somewhat disguising the actual point which I wanted to communicate. There is basically two important things that i wanted to talk about in this posting. First a slight improvement in T-SQL generation for Table Per Hierarchy from version 1 of EF. Secondly an existing smart T-SQL generation for Table Per Hierarchy which had always been there but i never noticed it. Let’s dwell into some of these features by starting with an existing model that i have already created.

Starting with Entity Framework 4.0 you can use Contains clause in your linq query to check if the column value matches any values in a given list. Suppose we have a model with Product and Category as shown below.

The title is a mouthful so let me explain what we are trying to solve. Suppose we have two tables in the database that have common fields. When we import the tables into Entity Data Model, we want to create a base entity to contain the common fields and let other entities derive from it. Since the base entity does not map to any table in particular in our database, we want to make base entity abstract. If you have reached this far and understood what the problem is, then follow along to know to solve it!

I am very happy to announce that Entity Framework 4.0 Recipes book by Apress is officially released and is available for purchase from Amazon and other online book retailers. You can get your copy from Amazon at the address below.