If, for example the Table and Column name are customized: For example, when using the following entity: I created a simple console application and ran a couple of tests to see if the data base was correctly created. It forces you to define the index name and gives the possibility of specifying whether the index is unique or not.Īnd the Initializer basically goes through the DbSet properties in the DbContext to retrieve the entity table names and check for the Index attribute in the properties in those entities. I found a couple of StackOverflow questions ( here and here) from where I got some really useful ideas, such as using the ExecuteSqlCommand method introduced in Entity Framework 4.1 and detecting the attributes in a DataBaseInitializer. By just looking at the entity you can determine the indexes that will be created for it, without the need to check a separate class' code. While developing your model changes a lot, so having to create an extra class whenever you discover that you want to add an index is not really confortable (once you have deployed to production however, migrations are probably the way to go). Code first migrations create a class per migration which results in too many classes.Update: After a quick twitter discussion with I decided to be more specific as to why I think using an attribute is better than code first migrations: Once I realized this, I decided to create the necessary components on my own. To my surprise, I wasn't able to find such an attribute when searching the web (for example, this is the list of available Data Annotations). Thus, I started to research to see if there where other ways to do this, thinking that there was probably an available data annotation to get this done. This approach successfully satisfied our requirements, but it required us to add additional migrations to specify the indexes. ![]() ![]() As we were also required to support changes to the model after the application was deployed, we decided to use Entity Framework Code Base Migrations. But it's not always the case that the names of the classes match the names of the tables in your database.This week, for a project at Southworks, my friend Mariano Converti and I had to create indexes in a SQL database for two string type properties of entities that were part of an Entity Framework Code First model. You can use Code First with an existing database. If you are letting Code First create the database, and also want to change the name of the tables it is creating. Tableĭefault Code First convention creates a table name similar to the class name. If the user sets the Title which contains more than 24 characters, then EF will throw EntityValidationError. Public DateTime EnrollmentDate Įntity Framework also validates the value of a property for StringLength attribute. So to handle this, a Key attribute is added which will make it a primary key. ![]() Let’s take a look at the following code of a Student class which contains StdntID, but it doesn’t follow the default Code First convention. You can use the key annotation to specify which property is to be used as the EntityKey. When Code First does not find a property that matches this convention, it will throw an exception because of Entity Framework’s requirement that you must have a key property. Now let’s suppose Student class used the name StdntID instead of ID. The Student, Course and Enrollment classes follow this convention. The property will map to a primary key column in the database. One of the conventions that Code First depends on is how it implies which property is the key in each of the Code First classes.Ĭonvention is to look for a property named “Id” or one that combines the class name and “Id”, such as “StudentId”. namespace includes the following attributes that impacts the schema of the database.Įntity Framework relies on every entity having a key value that it uses for tracking entities. includes the following attributes that impacts the nullability or size of the column. ![]() DataAnnotation attributes override default CodeFirst conventions. NET applications, such as ASP.NET MVC which allows these applications to leverage the same annotations for client-side validations. DataAnnotations are also understood by a number of. DataAnnotations is used to configure the classes which will highlight the most commonly needed configurations.
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