Entity Framework | .NET

Entity Framework:

   - Entity Framework is an Object-Relational Mapping (ORM) framework in .NET that simplifies database access by allowing you to work with database entities as if they were regular objects. Its purpose is to bridge the gap between object-oriented code and relational databases.

What are Code-First, Database-First, and Model-First approaches in Entity Framework?

   - Code-First: You define your data model in code first, and Entity Framework generates the database schema.

   - Database-First: You have an existing database schema, and Entity Framework generates entity classes based on it.

   - Model-First: You design your data model using a visual designer, and Entity Framework generates both the database schema and entity classes.

What is the role of `DbContext` in Entity Framework?

   - `DbContext` is a key class in Entity Framework that represents a session with the database. It's responsible for managing database connections, change tracking, and providing access to `DbSet` properties, which represent database tables.

4. What is Lazy Loading and Eager Loading in Entity Framework?

   - Lazy Loading: It's a feature that loads related entities from the database only when you access a navigation property. Lazy loading can lead to N+1 query problems.

   - Eager Loading: It's a technique to load related entities along with the main entity in a single query to avoid the N+1 query problem. You can use `Include` method or projection to achieve eager loading.

5. Explain the different states of entities in Entity Framework.

   - Entity Framework tracks the state of entities as Added, Unchanged, Modified, or Deleted. Understanding these states is crucial for managing changes to the database.

6. What is Entity Framework Core, and how does it differ from Entity Framework 6?

   - Entity Framework Core is a cross-platform, lightweight, and open-source version of Entity Framework. It's designed to work with .NET Core, but it can also run on the full .NET Framework. Differences include performance improvements, simplified APIs, and support for non-relational databases.

Migrations

To run migrations using Entity Framework (EF), you need to use the Entity Framework Migrations feature. Migrations allow you to manage changes to your database schema in a versioned and organized way. Here are the general steps to run migrations:

Step 1: Install Entity Framework Tools

Ensure that you have the Entity Framework tools installed. You can do this by installing the `Microsoft.EntityFrameworkCore.Tools` package using the following NuGet Package Manager Console command:

Install-Package Microsoft.EntityFrameworkCore.Tools

Step 2: Create Migrations

1. Open the Package Manager Console in Visual Studio (`Tools > NuGet Package Manager > Package Manager Console`).

2. Run the following command to create an initial migration:

Add-Migration InitialCreate

Replace "InitialCreate" with a meaningful name for your migration. This command generates a C# file in your project's "Migrations" folder that represents the changes needed to update the database schema.

Step 3: Apply Migrations

To apply the migrations and update the database schema:

1. Run the following command in the Package Manager Console:

Update-Database

This command will execute the pending migrations and apply the changes to the database.

Additional Migration Commands:

- To create a new migration after making changes to your data model or context, use `Add-Migration` with a different name:

Add-Migration MyNewMigration

- To specify the target database and connection string when applying migrations, you can use the `-ConnectionString` and `-TargetDatabase` parameters with `Update-Database`.

- You can also specify a particular migration to apply using `-Migration` with `Update-Database`. For example, to revert a migration, you can use `-Migration` to specify the migration name to which you want to roll back.

These are the basic steps to run migrations using Entity Framework. Migrations help you keep your database schema in sync with your application's data model as it evolves over time.

Scaffolding

Entity Framework provides a feature called "Database First" scaffolding, which allows you to generate entity classes and a context class based on an existing database schema. This is a useful approach when you already have a database, and you want to create the corresponding data access code in your application. Below are the steps to scaffold code using Entity Framework from an existing database:

.net core

Step 1: Install Entity Framework Core Tools

Ensure that you have Entity Framework Core Tools installed in your project. You can install it using the following command if you haven't already:

dotnet tool install --global dotnet-ef

Step 2: Create a .NET Core Console Application (Optional)

You can create a new .NET Core Console Application or use an existing project based on your needs.

Step 3: Create a Connection String

Make sure you have a connection string in your project's configuration (appsettings.json or another configuration file) that specifies the connection to your database. For example:

{

  "ConnectionStrings": {

    "MyDatabase": "Server=YourServer;Database=YourDatabase;User=YourUser;Password=YourPassword;"

  }

}

Step 4: Scaffold the Database

1. Open a command prompt or terminal in your project directory.

2. Run the following command to scaffold your database into your project:

dotnet ef dbcontext scaffold "Server=YourServer;Database=YourDatabase;User=YourUser;Password=YourPassword;" Microsoft.EntityFrameworkCore.SqlServer -o Models

- Replace `"Server=YourServer;Database=YourDatabase;User=YourUser;Password=YourPassword;"` with your actual connection string.

- `Microsoft.EntityFrameworkCore.SqlServer` specifies the database provider. You can change it to match the database you are using, such as `Microsoft.EntityFrameworkCore.Sqlite` for SQLite or `Pomelo.EntityFrameworkCore.MySql` for MySQL.

- `-o Models` specifies the output directory where the generated entity and context classes will be placed. You can change this to your preferred directory.

3. After running this command, Entity Framework will generate entity classes for your database tables in the specified output directory. It will also create a DbContext class that you can use to interact with the database.

Step 5: Use the Generated Code

You can now use the generated code in your application to interact with the database. The generated DbContext class will allow you to query and manipulate data in your database using LINQ queries and methods.

Remember to also configure and add any necessary dependencies, such as the Entity Framework Core package and the database provider package, to your project's `csproj` file.

That's it! You've scaffolded code using Entity Framework from an existing database, and you can now work with your database using the generated classes and context.

.net

In .NET Framework 4.5 (not .NET Core), you can use Entity Framework's Database First approach to scaffold code from an existing database. Here's how you can do it:

Step 1: Create a .NET Framework Project

Create a new or use an existing .NET Framework project (e.g., a Windows Forms, WPF, ASP.NET, or Console Application).

Step 2: Install Entity Framework

If you haven't already, you need to install Entity Framework using NuGet Package Manager:

Install-Package EntityFramework

Step 3: Create a Connection String

Make sure you have a connection string in your project's configuration (usually in the `App.config` or `Web.config`) that specifies the connection to your database. For example:

<connectionStrings>

    <add name="YourDbContext" connectionString="Server=YourServer;Database=YourDatabase;User=YourUser;Password=YourPassword;" providerName="System.Data.SqlClient" />

</connectionStrings>

Replace the connection string values with your actual database connection details.

Step 4: Scaffolding the Database

1. Open the Visual Studio Package Manager Console (`View > Other Windows > Package Manager Console`).

2. Run the following command to scaffold your database into your project:

Scaffold-DbContext "Server=YourServer;Database=YourDatabase;User=YourUser;Password=YourPassword;" System.Data.SqlClient -OutputDirectory Models

- Replace the connection string `"Server=YourServer;Database=YourDatabase;User=YourUser;Password=YourPassword;"` with your actual connection string.

- `-OutputDirectory Models` specifies the output directory where the generated entity classes and DbContext will be placed. You can change this to your preferred directory.

3. Entity Framework will generate entity classes for your database tables in the specified output directory. It will also create a DbContext class that you can use to interact with the database.

Step 5: Use the Generated Code

You can now use the generated code in your .NET Framework application to interact with the database. The generated DbContext class will allow you to query and manipulate data in your database using LINQ queries and methods.

Remember to configure and add the necessary dependencies, such as Entity Framework, to your project's references.

This approach is specific to .NET Framework 4.5 and earlier versions. For .NET Core and later versions of .NET, the process is different and uses the Entity Framework Core tools.

Execute stored procedure 

To execute a stored procedure using Entity Framework in a .NET application, you can follow these steps:

Step 1: Define a DbContext

Ensure that you have a DbContext class in your project that represents your database context. This class should inherit from `DbContext` and contain a DbSet for each entity you need to work with.

public class YourDbContext : DbContext

{

    public YourDbContext(DbContextOptions<YourDbContext> options)

        : base(options)

    {

    }

    // DbSet properties for your entities

    public DbSet<Customer> Customers { get; set; }

    // Add more DbSet properties as needed

}

Step 2: Define a Model for the Stored Procedure Result

Create a class that represents the structure of the result set returned by your stored procedure.

public class StoredProcedureResult

{

    public int Column1 { get; set; }

    public string Column2 { get; set; }

    // Add properties to match the result set columns

}

Step 3: Execute the Stored Procedure

You can execute the stored procedure using the `FromSqlRaw` or `FromSqlInterpolated` method provided by Entity Framework. Here's how to do it:

using System.Collections.Generic;

using System.Linq;

using Microsoft.EntityFrameworkCore;

public class YourRepository

{

    private readonly YourDbContext _context;

    public YourRepository(YourDbContext context)

    {

        _context = context;

    }

    public List<StoredProcedureResult> ExecuteStoredProcedure()

    {

        // Use the FromSqlRaw method to execute the stored procedure

        return _context.StoredProcedureResults.FromSqlRaw("EXEC YourStoredProcedureName @param1, @param2", 

                                                           new SqlParameter("@param1", value1),

                                                           new SqlParameter("@param2", value2))

                                             .ToList();

    }

}

- Replace `YourStoredProcedureName` with the name of your stored procedure.

- Provide the appropriate parameters using `SqlParameter` objects.

- `StoredProcedureResults` should match the structure of the result set columns from your stored procedure.

Step 4: Use the Executed Data

You can now call the `ExecuteStoredProcedure` method from your application code to execute the stored procedure and retrieve the results. You can work with the returned data as needed.

Make sure to register your DbContext and repository in your application's dependency injection container if you're using one.

This approach allows you to execute a stored procedure and retrieve its results using Entity Framework in your .NET application.

Execute stored procedure with DataTable

To send data to a stored procedure using a `DataTable` in C#, you can follow these steps:

Step 1: Create a DataTable

Create a `DataTable` and add rows with the data you want to pass to the stored procedure. Make sure that the column names in the `DataTable` match the parameter names expected by the stored procedure.

DataTable dataTable = new DataTable();

dataTable.Columns.Add("Param1", typeof(int));

dataTable.Columns.Add("Param2", typeof(string));

// Add rows to the DataTable

dataTable.Rows.Add(1, "Value1");

dataTable.Rows.Add(2, "Value2");

// Add more rows as needed

Step 2: Set Up a SqlCommand

Create a `SqlCommand` to execute the stored procedure. Make sure to specify the CommandType as `CommandType.StoredProcedure`, set the stored procedure name, and add parameters corresponding to your DataTable.

using (SqlConnection connection = new SqlConnection("YourConnectionString"))

{

    connection.Open();

    

    using (SqlCommand cmd = new SqlCommand("YourStoredProcedureName", connection))

    {

        cmd.CommandType = CommandType.StoredProcedure;

        

        // Add parameters that match the structure of your DataTable

        cmd.Parameters.Add(new SqlParameter("@ParamTable", dataTable)

        {

            SqlDbType = SqlDbType.Structured,

            TypeName = "YourTableTypeName" // Replace with your user-defined table type name

        });

        

        cmd.ExecuteNonQuery();

    }

}

- Replace `"YourConnectionString"` with your database connection string.

- `"YourStoredProcedureName"` should be replaced with the name of your stored procedure.

- `"YourTableTypeName"` should be replaced with the name of your user-defined table type (if your stored procedure expects a user-defined table type).

Step 3: Configure SQL Server Table-Valued Parameter (TVP)

In SQL Server, you need to define a User-Defined Table Type that matches the structure of your DataTable. You should create this table type in your database using SQL Server Management Studio or a script.

Here's an example of defining a User-Defined Table Type:

```sql

CREATE TYPE dbo.YourTableTypeName AS TABLE

(

    Param1 INT,

    Param2 NVARCHAR(MAX)

);

Ensure that the structure of the table type matches the columns you added to your `DataTable`.

Step 4: Modify the Stored Procedure

Modify your stored procedure to accept the User-Defined Table Type as a parameter. You can then use this table type within your stored procedure to work with the data sent from C#. Here's an example of how your stored procedure might look:

```sql

CREATE PROCEDURE YourStoredProcedureName

(

    @ParamTable YourTableTypeName READONLY -- Use the table type you defined

)

AS

BEGIN

    -- Your stored procedure logic here

    -- You can use @ParamTable just like a regular table within your procedure

END

```

Now, when you execute the C# code with the `DataTable` as a parameter, it will send the data to the stored procedure, and you can work with it inside the stored procedure logic.