These sets are automatically initialized when the instance of the derived class is created. This behavior can be modified by applying the SuppressDbSetInitializationAttribute attribute to either the entire derived context class, or to individual properties on the class.
The Entity Data Model backing the context can be specified in several ways. The protected OnModelCreating method can be overridden to tweak this model.
More control over the model used for the Model First approach can be obtained by creating a DbCompiledModel explicitly from a DbModelBuilder and passing this model to one of the DbContext constructors. The connection to the database including the name of the database can be specified in several ways. If the parameterless DbContext constructor is called from a derived context, then the name of the derived context is used to find a connection string in the app.
If no connection string is found, then the name is passed to the DefaultConnectionFactory registered on the Database class. The connection factory then uses the context name as the database name in a default connection string. This default connection string points to. Note that the connection found in the app. A DbModelBuilderVersionAttribute can be applied to a class derived from DbContext to set the version of conventions used by the context when it creates a model.
If no attribute is applied then the latest version of conventions will be used. Constructs a new context instance using conventions to create the name of the database to which a connection will be made. See the class remarks for how this is used to create a connection. Constructs a new context instance using conventions to create the name of the database to which a connection will be made, and initializes it from the given model.
Constructs a new context instance using the existing connection to connect to a database. The connection will not be disposed when the context is disposed if contextOwnsConnection is false. Constructs a new context instance using the existing connection to connect to a database, and initializes it from the given model.
Constructs a new context instance using the given string as the name or connection string for the database to which a connection will be made. If you are working with the EF Designer, the context will be generated for you.
If you are working with Code First, you will typically write the context yourself. Adding a new object with Entity Framework is as simple as constructing a new instance of your object and registering it using the Add method on DbSet. The following code is for when you want to add a new student to database.
Changing existing objects is as simple as updating the value assigned to the property s you want changed and calling SaveChanges. In the following code, the last name of Ali has been changed from Khan to Aslam. Remove works for both existing and newly added entities. Calling Remove on an entity that has been added but not yet saved to the database will cancel the addition of the entity.
In the Get method, it will return an employee based on the ID. Whereas, in the GetAll method it will return the list of all the employees in the database. We will need to add a connection string so that our DBContext knows which server to go to and which database to query. NET and the MVC framework, the Entity Framework relies on dependency injection, and for injection to work, the runtime needs to know about the various services that the Entity Framework uses.
Let us go to the AppSettings. Let us now go to the Startup class where we need to add some additional services for the Entity Framework to work properly. All this can be done through methods that are available as extension methods on IServiceCollection as shown in the following program. The first method is the AddEntityFramework. This will add the core Entity Framework services, the default services. But since the Entity Framework is now designed to work with different sorts of databases, including non-relational databases, we need to make a second call to tell the Entity Framework to add its default SQL Server-related services.
Then we also need to tell the Entity Framework about my DBContext class so it can construct instances of that class appropriately and we can do that through a third method, the AddDbContext method. This can be done by a lambda expression ; it is an action where we receive an option parameter and the Entity Framework can support the different databases.
Now we need to set up the database. The migration code is C code. This can be executed to create a database in a database schema. The Entity Framework looks at the database and at our models and figures out what the schema changes are required to make the application work.
So when we add additional models or make changes to the existing models, like the Employee class, we can continue to add migrations to our project and keep our database schema in sync. That is why we have made project. Let us open the Developer Command Prompt for Visual Studio to run the commands that we need to add the migrations and apply the migrations.
The easiest way to do this is to go to the application root directory.
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