Question

条件将仅在运行时指定

我尝试使用一个条件动态地连接两个表，它工作正常。但动态有两个或两个以上的条件，它不起作用。请帮我解决这个问题

请查看案例

案例1：加入一个条件（正常工作）

Base entity:User

entity to join :Role

condition to join: Role.Id = User.RoleId


//select * from User inner join Role on User.RoleId=Role.Id

//static way

     IQueryable<UserEntity> query =
        db.Set<user>().Join(db.Set<Role>(), 
        user =>  User.RoleId, 
        role=> role.Id, 
        (user , role) => new { user , role }).Select(temp=> temp.user);



//Dynamic Way **(working fine)**           


 ParameterExpression lambdaExprVar_Role = Expression.Parameter(typeof(Role), "role");

            PropertyInfo rightPropertyInfo_role = typeof(Role).GetProperty("Id");

            Expression rightExpression_role = Expression.Property(lambdaExprVar_Role, rightPropertyInfo_role );

            Expression<Func<Role, Int64>> myexp_role = Expression.Lambda<Func<Role, Int64>>(rightExpression_role , new ParameterExpression[] { lambdaExprVar_Role });                  

            ParameterExpression lambdaExprVar_User = Expression.Parameter(typeof(User), "user");

            PropertyInfo rightPropertyInfo_user = typeof(User).GetProperty("RoleId");

            Expression rightExpression_user = Expression.Property(lambdaExprVar_User, rightPropertyInfo_user);

            Expression<Func<User, Int64>> myexp_user = Expression.Lambda<Func<User, Int64>>(rightExpression_user, new ParameterExpression[] { lambdaExprVar_User });       

    IQueryable<OrganizationNode> query = db.Set<User>()
                .Join(db.Set<Role>(), myexp_user, myexp_role, (user, role) => new {user, role})
                .Select(temp=>temp.user);

案例2：加入两个条件（不工作）

Base entity:User

entity to join :Role

condition to join: Role.Id==User.RoleId,Role.Code==User.RoleCode

//select * from User inner join Role on User.RoleId=Role.Id and User.RoleCode=Role.Code

//static way **(working fine)**



    IQueryable<User> query =
        db.Set<user>().Join(db.Set<Role>(), 
        **user => new { matchId = user.RoleId, matchcode= user.RoleCode}, 
        role=> new { matchId = role.Id, matchcode= role.code},** 
        (user , role) => new { user , role }).Select(temp=> temp.user);

//Dynamic Way   (**** not working)

帮我写/重写代码。

Answer 1

试试这个

from u in db.Set<user>
inner join r in db.Set<Role>
on new {r.Id, r.Code} equals {u.RoleId, u.RoleCode)
select u

编写上述linq查询的另一种方法如下：

from u in db.Set<user>
from r in db.Set<Role>.Where(r.Id==RoleId && u.RoleCode==r.Code)
select u

用于连接具有多个条件的两个表的动态Linq查询（动态）

1 个答案: