Entity Framework -- Linq To Entity使用方式

1. Projection

using(var ctx=new SchoolEntities())
{
    ObjectQuery<Courses> courses = ctx.Courses;
    IQueryable<Courses> allcourses = from c in courses
                                     select c;
    Console.WriteLine(courses.ToTraceString());
}

2. Where

using(var ctx=new SchoolEntities())
{
    ObjectQuery<Courses> courses = ctx.Courses;
    IQueryable<Courses> allcourses = from c in courses
                                     where c.CourseName == "Act"
                                     select c;
}

3.Pagination

using(var ctx=new SchoolEntities())
{
    ObjectQuery<Courses> courses = ctx.Courses;
    IQueryable<Courses> allcourses = from c in courses
                                     orderby c.CourseType
                                     select c.Skip(0).Take(100);
}

4. Aggregation (Average, Max, Min, Count, Sum)

using(var ctx=new SchoolEntities())
{
    var older = ctx.Persons.Max(p=>p.Age);
    Console.WriteLine(older.Value);
}

5. Join

using(var ctx=new SchoolEntities())
{
    var query = from c in ctx.Courses
                join d in ctx.CourseDetails
                on d.CourseID equals c.CourseID
                select new{
                    c, d.Info};
}