关系型数据之LinQ基本查询

如下图所示关系型数据,LinQ语句为:

var Query= from a in data.Awhere a.admin==传入的用户名&&a.pwd==传入的密码(可以传入一个model实体)
join b in data.B
            on a.bid equals b.id into ab
from r1 in ab.DefaultIfEmpty()
            join c in data.C
            on r1.cid equals c.id into bc
from r2 in bc.DefaultIfEmpty()
            join d in data.D
            on r2.did equals d.id into cd
from r3 in cd.DefaultIfEmpty()

select new            {

//这里是table A 的id;
                  Id = a.Id,

//这里是table B的Name;
                  Name = r1.Name,
                  Pro = r2.Pro,
                  IpAdd = r3.IpAdd
            };

//转成数组形式;

var list = Query.ToList();

//list[0].Name即表示整个LinQ查询的结果的第一条数据的table B的Name,以此类推;

 

注: r1可以.出table B的所有数据...以此类推;

r2==table C;

r3==table D;

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1、左连接：

var LeftJoin = from emp in ListOfEmployees
join dept in ListOfDepartment
on emp.DeptID equals dept.ID into JoinedEmpDept
from dept in JoinedEmpDept.DefaultIfEmpty()
select new                        
{
EmployeeName = emp.Name,
DepartmentName = dept != null ? dept.Name : null                        
};

 

2、右连接：

var RightJoin = from dept in ListOfDepartment
join employee in ListOfEmployees
on dept.ID equals employee.DeptID into joinDeptEmp
from employee in joinDeptEmp.DefaultIfEmpty()
select new                          
{
EmployeeName = employee != null ? employee.Name : null,
DepartmentName = dept.Name
};

 

3、内连接：

 var query = from t in entitiy.TB_GCGL_ADA_USER
                 join p in entitiy.TB_GCGL_ZY_ZYK
                 on t.ETPRS_CODE equals p.ETPRS_CODE

                 select new TB_USER_ZYK
                 {
                    USER_ID = t.USER_ID,
                    USER_NAME = t.USER_NAME,
                    USER_PASSWORD = t.USER_PASSWORD,

                 };