在LINQ动态where子句？ [英] Dynamic where clause in LINQ?

问题描述

我试图加载基于动态WHERE条件的数据。

I am trying to load data based on Dynamic where condition.

string tempQry = string.Empty;
if (!string.IsNullOrEmpty(cusid) && !string.IsNullOrEmpty(mktid))
    tempQry = "x=>x.MarketID==" + mktid + "&& x.MasterCustomerID==" + cusid;
if (string.IsNullOrEmpty(cusid)) 
    tempQry = "x=>x.MarketID==" + mktid;
if (string.IsNullOrEmpty(mktid)) 
    tempQry = "x=>x.MasterCustomerID==" + cusid;

_lstOptInInterest = new LinkedList<OptInInterestArea>(
        (from a in _lstOptInInterest
         join b in _marketoEntities.CustCommPreferences.Where(tempQry)
         on new { CODE = a.Code, SUBCODE = a.SubCode } equals new { CODE = b.Option_Short_Name, SUBCODE = b.Option_Short_Subname }
         into leftGroup
         from b in leftGroup.DefaultIfEmpty()
         select new OptInInterestArea()
         {
             Code = a.Code,
             SubCode = a.SubCode,
             SubCodeDescription = a.SubCodeDescription,
             CodeDescription = a.CodeDescription,
             PrevOptIn = b != null && b.OptedIn == true
         }).ToList());

这是给编译错误凡（tempQry）。


'System.Data.Entity.DbSet< Market.Data.CustCommPreference>'不包含定义去哪儿和最好的推广方法重载'System.Linq.Queryable.Where< TSource>（System.Linq.IQueryable< TSource>中System.Linq.Expressions.Expression< System.Func< TSource，布尔>>）'有一些无效参数

如何处理呢？

推荐答案

其中，等待条件lambda表达式而不是字符串的形式，让你必须重构你的代码一点点（以下只是一个想法）：

Where awaits conditions in form of lambdas rather than strings, so you have to refactor your code a little bit (just an idea below):

IQueryable<CustCommPreference> query = _marketoEntities.CustCommPreferences.AsQueryable();
if (!string.IsNullOrEmpty(cusid)) 
    query = query.Where(x => x.MasterCustomerID == cusid);
if (!string.IsNullOrEmpty(mktid)) 
    query = query.Where(x => x.MarketID == mktid);

和以后使用它：

...
join b in query
...

这篇关于在LINQ动态where子句？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！