多個條件Linq擴展

Question

我需要考慮多個條件才能獲得價值。 我的意思是，如果所有條件都是真的，必須給我一個過濾的答案。 或者其中一個是真的，其餘都是假的... 所以我需要寫所有的可能性？ 如果（一個& b &Ç& d）否則如果（一個& b & C）否則如果（一個&ç& d）否則如果（B &Ç& d）否則如果（一個& B）否則如果（一個& c）...等等:)））有沒有更簡單的方法來做到這一點？

public List<ProductReqNoDate> GetRequestsQuery(string departmant, int reqStateID, string firstDate, string lastDate, string productName) 
    { 
     var db = new requestDBEntities(); 
     bool dp = !string.IsNullOrEmpty(departmant); 
     bool pr = !string.IsNullOrEmpty(productName); 
     bool tm = !string.IsNullOrEmpty(firstDate) && !string.IsNullOrEmpty(lastDate); 
     bool rs = reqStateID > 0 ? true : false; 

     var query = (from r in db.requests 
        select new ProductReqNoDate 
        { 
         departmant = r.departmant, 
         reqNo = r.reqNo, 
         reqDate = r.reqDate, 
         productName = (from p in db.products where p.reqNo == r.reqNo select p.productName).FirstOrDefault() 
        }).ToList(); 
     if (dp & pr & tm & rs) 
     { 
      var rState = (from ta in db.reqStates 
          where ta.reqStateID == reqStateID && ta.isActive == true 
          select ta.reqNo).ToList(); 
      var prName = (from p in db.products where p.productName.Contains(productName) select p.reqNo).ToList(); 
      DateTime dtfirstDate = Convert.ToDateTime(firstDate); 
      DateTime dtlastDate = Convert.ToDateTime(lastDate); 

      return query.Where(
       r => rState.Contains(r.reqNo) //find by Request State 
        && r.departmant == departmant //find by Departmant 
        && (r.reqDate >= dtfirstDate && r.reqDate <= dtlastDate) //find by Date 
        && prName.Contains(r.reqNo) //Find By Product Name 
        ).ToList(); 

     } 
     else if (dp & pr & tm) { /*return query.Where(...} */} 
     else if (pr & tm & rs) { /*return query.Where(...} */} 
     else if (dp & pr && rs) { /*return query.Where(...} */} 
     else if (dp & pr) { /*return query.Where(...} */} 
     //else if ...etc 
    } 

Answer 1

只需添加一個凡在同一時間

public List<ProductReqNoDate> GetRequestsQuery(string departmant, int reqStateID, string firstDate, string lastDate, string productName) 
{ 
    var db = new requestDBEntities(); 
    bool dp = !string.IsNullOrEmpty(departmant); 
    bool pr = !string.IsNullOrEmpty(productName); 
    bool tm = !string.IsNullOrEmpty(firstDate) && !string.IsNullOrEmpty(lastDate); 
    bool rs = reqStateID > 0 ? true : false; 

    var query = (from r in db.requests 
       select new ProductReqNoDate 
       { 
        departmant = r.departmant, 
        reqNo = r.reqNo, 
        reqDate = r.reqDate, 
        productName = (from p in db.products where p.reqNo == r.reqNo select p.productName).FirstOrDefault() 
       }).AsQueryable(); //AsQueryable is not always needed, but it shouldn't hurt and I don't feel like checking for this example. 


    if (dp) 
    { 
     query = query.Where(q => /*condition*/); 
    } 

    if (pr) 
    { 
     query = query.Where(q => /*condition*/); 
    } 

    if (tm) 
    { 
     query = query.Where(q => /*condition*/); 
    } 

    if (rs) 
    { 
     query = query.Where(q => /*condition*/); 
    } 

    return query.ToList(); 
} 

Answer 2

你可以建立一個表達Expression.And，如：

private Expression<Func<Request, bool>> GetPredicate(FilterDto filter) 
{ 
    Expression<Func<Request, bool>> predicate = r => r.ID == r.ID; 

    if (filter.Department.HasValue) 
    predicate = predicate.And(r => r.Department == filter.Department.Value); 
    if (filter.FirstDate.HasValue) 
    predicate = predicate.And(r => (r.reqDate >= filter.FirstDate.Value)); 
    if (filter.LastDate.HasValue) 
    predicate = predicate.And(r => (r.reqDate <= filter.LastDate.Value)); 

    /* ... */ 

    return predicate; 
} 

注：我把r => r.ID == r.ID這裏第一個表達式，只是將不得不開始與表達。這段代碼並沒有完全覆蓋你的代碼，但我認爲這足以作爲一個例子。

使用return query.Where(expression).ToList()中的表達式。