Lambda expressions join syntax how to understand-CodePudding

Public List GetMenusByRoleId (string roleId)
{
Using (var scope=_dbContextScopeFactory CreateReadOnly ())
{
Var db=scope. DbContexts. Get (a);
Var list=db. Menus. The Where (m=& gt; ! M.I sDeleted)
.join (db) RoleMenus, m=& gt; M.I d, rm=& gt; Rm. MenuId, (menu, roleMenu)=& gt; New {menu, roleMenu})
The Where (item=& gt; Item. RoleMenu. RoleId==RoleId)
The Select (item=& gt; Item. The menu). ToList ();
Return _mapper. Map List (list);
}
}

One. Join (db RoleMenus, m=& gt; M.I d, rm=& gt; Rm. MenuId, (menu, roleMenu)=& gt; New {menu, roleMenu}) how to understand,
Is there a detailed explanation on this,
Feeling linq is easier to understand,

CodePudding user response:

Open it,
A. oin (b,,,,,,,,
A table b table

M=& gt; M.I d, rm=& gt; The rm MenuId,
Id in a table, where m is just a generation refers to
By the same token, the rm representative id, b
Is associated with the column id,

(menu, roleMenu)
The returned result set

//abstract: 
//Correlates the elements of two sequences -based on matching keys. 
//equality comparer is 2 compare keys. 
//
//parameters: 
//outer: 
//The first sequence to join. 
//
//inner: 
//The sequence to join to The first sequence. 
//
//outerKeySelector: 
//A function to extract the join key from each element of the first sequence. 
//
//innerKeySelector: 
//A function to extract the join key from each element of the second sequence. 
//
//resultSelector: 
//A function to create A result element from two matching elements.

CodePudding user response:

However, although I use lambda more at ordinary times,
But about the join such, I still use linq,
I personally feel looks more transparent,
I might write

 
Var q=(from a in a 
Join in on Anderson d b b equals b.i d 
The where... 
Select (new {a, b}) 
). ToList () 
//after may also to lambda 
The where (x=& gt; . ) 
. Take...