https://ask.csdn.net/questions/194677
ef join 用法
var customers = DB.Customer.Join(DB.Commission, cst => cst.CommissionId,
com => com.CommissionId, (cst, com) => new Customer()
{
CommissionId = com.CommissionId,
CustomerId = cst.CustomerId,
CustomerName = cst.CustomerName,
ERPCustomerNo = cst.ERPCustomerNo,
UserId = cst.UserId
}).ToList();