entity framework 中一些常用的函数 转自http://www.cnblogs.com/williamzhu/
2015-05-11 16:50
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一般查询
var Courses = db.Courses.Where(c => c.Title == "Physics").OrderBy(c => c.Title); foreach (var c in Courses) { Console.WriteLine(c.Title); }
添加
Models.Course model = new Course(); model.Title = "test"; model.DepartmentID = 1; model.CourseID = 4; db.Courses.Add(model); db.SaveChanges();
修改
Models.Course model = new Course(); var result = (from r in db.Courses where r.Title.StartsWith("test") orderby r.Title descending select r).FirstOrDefault(); model = (Course)result; model.Credits = 4; model.Title = "good job"; db.SaveChanges();
删除
var result = from r in db.Courses where r.CourseID == 4 select r; foreach (var c in result) { db.Courses.Remove(c); } db.SaveChanges();
简单的函数计算(count,min,max,sum)
var result = (from r in db.StudentGrades where r.StudentID == 2 select r).Sum(p=>p.Grade); Console.WriteLine(result); var result = (from r in db.StudentGrades where r.StudentID == 2 select r).Max(p => p.Grade); Console.WriteLine(result);
分页数据查询
var result = (from r in db.People orderby r.LastName ascending select r).Skip(5).Take(5); foreach(var c in result) { Console.WriteLine(c.LastName); }
分组group by
var ss = from r in db.StudentGrades orderby r.StudentID descending group r by new { r.StudentID, r.CourseID } into g select new { g.Key, grade = g.Sum(r => r.Grade) }; foreach (var r in ss) { string output = "StudentID:" + r.Key.StudentID + " CourseID:" + r.Key.CourseID+" grade"+r.grade; Console.WriteLine(output); }
复杂的关联查询
var d = db.Database.SqlQueryForDynamic(@"SELECT c.CourseID,d.[Name] as department,c.Title FROM Course c INNER JOIN Department d ON c.DepartmentID = d.DepartmentID"); foreach (dynamic item in d) { var s = item.Title; Console.WriteLine(s); } Console.ReadLine();
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