Entity Framework Tutorial Basics（39）：Raw SQL Query

Execute Native SQL Query

You can execute native raw SQL query against the database using DBContext. You can execute the following types of queries:

1. SQL query for entity types which returns particular types of entities
2. SQL query for non-entity types which returns a primitive data type
3. Raw SQL commands to the database

SQL query for entity types:

As we have seen in one of the previous chapters, DBSet has SQLQuery() method to write raw SQL queries which return entity instances. The returned objects will be tracked by the context, just as they would be if they were returned by a LINQ query. For example:

using (var ctx = new SchoolDBEntities())
{
    var studentList = ctx.Students.SqlQuery("Select * from Student").ToList<Student>();

}

However, columns returned by SQL query should match the property of an entity type of DBSet otherwise, it will throw an exception. For example:

using (var ctx = new  SchoolDBEntities())
{
    var studentName = ctx.Students.SqlQuery("Select studentid, studentname
        from Student where studentname='New Student1'").ToList();

}

If you change the column name in query, then it will throw an exception because it must match column names:

using (var ctx = new SchoolDBEntities())
{
    //this will throw an exception
    var studentName = ctx.Students.SqlQuery("Select studentid as id, studentname as name
            from Student where studentname='New Student1'").ToList();
}

SQL query for non-entity types:

A SQL query returning instances of any type, including primitive types, can be created using the SqlQuery method on the Database class. For example:

using (var ctx = new SchoolDBEntities())
{
    //Get student name of string type
    string studentName = ctx.Database.SqlQuery<string>("Select studentname
        from Student where studentid=").FirstOrDefault<string>();
}

Raw SQL commands to the database:

ExecuteSqlCommnad method is useful in sending non-query commands to the database, such as the Insert, Update or Delete command. For example:

using (var ctx = new SchoolDBEntities())
{

    //Update command
    int noOfRowUpdated = ctx.Database.ExecuteSqlCommand("Update student
            set studentname ='changed student by command' where studentid=");
    //Insert command
    int noOfRowInserted = ctx.Database.ExecuteSqlCommand("insert into student(studentname)
            values('New Student')");
    //Delete command
    int noOfRowDeleted = ctx.Database.ExecuteSqlCommand("delete from student
            where studentid=");

}