Defining custom SQL query for entity

Sometimes, you may need to define custom SQL queries to retrieve entities from the database in Entity Framework. This can be useful when you have complex queries that cannot be easily expressed using the standard LINQ queries.

Follows the steps below to define a custom SQL query for an entity.

Step 1: Create a Custom SQL Provider

To define a custom SQL query, start by creating a class that implements the ISqlProvider<TEntity> interface. This interface defines a method, GetQuerySql(), where you can specify your custom SQL query.

private class BlogSqlProvider : ISqlProvider<Blog>
{
    public SqlString GetQuerySql() => SqlString.FromSqlInterpolated($"SELECT \"Id\", \"Name\" FROM \"Blog\"");
}

In this example, we've created a BlogSqlProvider class that implements the ISqlProvider<Blog> interface and defines a custom SQL query for retrieving blog entities.

Step 2: Implement the GetQuerySql() Method

Inside your custom SQL provider class, implement the GetQuerySql() method. This method should return a SqlString instance containing your raw or interpolated SQL query. Customize the query to match your specific requirements and entity structure.

Step 3: Register the Custom SQL Provider

To make your custom SQL provider available for dependency injection, you need to register it with your application's service container. You need to register it using the singleton lifetime, as show below:

services.AddSingleton<ISqlProvider, BlogSqlProvider>();

In this registration, we specify the interface ISqlProvider and its corresponding implementation BlogSqlProvider. This allows the Raiqub.Expressions to resolve and use your custom SQL provider when needed.

Best Practices

• Keep Queries Simple: While custom SQL queries provide flexibility, it's essential to keep them as simple and readable as possible. Avoid complex queries that can be hard to maintain.
• Use Parameters: If your custom query requires input parameters, use parameterized queries to prevent SQL injection and improve performance.
• Test Thoroughly: Custom SQL queries may bypass some of Entity Framework's built-in protections. Ensure thorough testing to validate the correctness and security of your queries.