Overview

Using advanced features of Entity Framework (EF) like stored procedures and table-valued functions (TVFs) allows for optimized data access and manipulation, thus combining the benefits of EF's ORM capabilities with the power and efficiency of raw SQL operations. Understanding how to implement and use these features is crucial for developers who aim to build high-performance, scalable applications with complex data requirements.

Key Concepts

• Stored Procedures: Precompiled SQL queries stored in a database that can perform complex operations and return results. They are beneficial for encapsulating business logic, optimizing performance, and enhancing security.
• Table-Valued Functions (TVFs): Functions that return a table data type and can be queried like a regular table. TVFs are useful for encapsulating complex, reusable query logic.
• Entity Framework Execution Methods: Understanding how to execute stored procedures and TVFs within the EF context, including using the Database.SqlQuery, DbSet<TEntity>.FromSql, and DbSet<TEntity>.SqlQuery methods for querying and the Database.ExecuteSqlCommand for non-query executions.

Common Interview Questions

Basic Level

1. How do you call a stored procedure in Entity Framework?
2. What is a Table-Valued Function (TVF), and how can it be used in EF?

Intermediate Level

3. How can you map the results of a stored procedure to an entity in EF?

Advanced Level

4. What are the performance considerations when using stored procedures and TVFs in EF?

Detailed Answers

1. How do you call a stored procedure in Entity Framework?

Answer: To call a stored procedure in Entity Framework, you can use the DbContext.Database.SqlQuery method for queries that return entities or the DbContext.Database.ExecuteSqlCommand for stored procedures that perform updates, deletes, or inserts without returning a dataset.

Key Points:
- The Database.SqlQuery method is used for stored procedures that return entities or other types of data.
- The Database.ExecuteSqlCommand is used for non-query stored procedures.
- It's important to match the return type of the stored procedure with the method used.

Example:

public IEnumerable<Product> GetProductsByCategory(string category)
{
    // Using SqlQuery for a stored procedure that returns data
    return this.Database.SqlQuery<Product>("spGetProductsByCategory @p0", category).ToList();
}

public void UpdateProductPrice(int productId, decimal newPrice)
{
    // Using ExecuteSqlCommand for a stored procedure that does not return data
    int result = this.Database.ExecuteSqlCommand("spUpdateProductPrice @p0, @p1", productId, newPrice);
}

2. What is a Table-Valued Function (TVF), and how can it be used in EF?

Answer: A Table-Valued Function (TVF) is a function in SQL Server that returns a table data type. In Entity Framework, you can use TVFs by calling them directly in a LINQ query, allowing you to compose over the results returned by the TVF as if it were a regular table or query.

Key Points:
- TVFs can be used in LINQ queries to compose over the results.
- EF allows querying a TVF as it would any other DbSet or IQueryable.
- TVFs provide a way to encapsulate complex logic in the database layer and expose it in a way that's easily consumable by EF.

Example:

public IQueryable<Product> GetProductsByCategory(string category)
{
    // Assuming there's a TVF named "fnGetProductsByCategory" that returns products
    return this.Database.SqlQuery<Product>("SELECT * FROM fnGetProductsByCategory(@p0)", category).AsQueryable();
}

3. How can you map the results of a stored procedure to an entity in EF?

Answer: To map the results of a stored procedure to an entity in Entity Framework, you should ensure that the stored procedure returns columns that match the properties of the entity. If the names or types do not match, you may need to adjust the stored procedure or use an intermediary model to capture the results and then map to your entity.

Key Points:
- The stored procedure's result set columns must match the entity's properties in name and type.
- You can use the DbContext.Database.SqlQuery<TEntity> method for direct mapping.
- For complex mappings or when names/types do not match, use an intermediary DTO (Data Transfer Object) and then map to the entity.

Example:

public IEnumerable<Customer> GetAllCustomers()
{
    // Directly mapping the result to the Customer entity
    return this.Database.SqlQuery<Customer>("spGetAllCustomers").ToList();
}

4. What are the performance considerations when using stored procedures and TVFs in EF?

Answer: When using stored procedures and TVFs with Entity Framework, consider performance implications like the potential for SQL injection, execution plan caching, and the overhead of marshaling data between the database and the application. Properly using these features can lead to significant performance gains, especially in complex queries or bulk operations.

Key Points:
- Stored procedures and TVFs can leverage SQL Server execution plan caching for faster performance on repeated calls.
- Overuse can lead to increased complexity and potentially hinder EF's ability to track changes in entities.
- Proper parameterization is crucial to avoid SQL injection vulnerabilities.

Example:

// Example showing parameterized query to avoid SQL injection
public IEnumerable<Product> GetProductsByCategory(string category)
{
    return this.Database.SqlQuery<Product>("SELECT * FROM fnGetProductsByCategory(@p0)", new SqlParameter("@p0", category)).ToList();
}