LinQ查詢Simple Where子句和許多過濾條件

Question

我需要過濾數據實體，但沒有預定義的列，我將不得不過濾。

public class EventDocument
{
    public string ID1 { get; set; }
    public int ID2 { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Number { get; set; }
    public virtual ICollection<Event> Events { get; set; }
}

我創建了所有需要的屬性：SearchFirstName，SearchLastName，SearchNumber

現在我試圖通過用戶輸入的這些參數來過濾EventDocument。 如果用戶在SearchFirstName中輸入值，我的查詢將如下所示：

var query = from b in DBContext.EventDocuments
                    where b.FirstName.Contains(SearchFirstName)
                    select b;

如果用戶輸入SearchFirstName和SearchLastName的值，我的查詢將如下所示：

var query = from b in DBContext.EventDocuments
                        where b.FirstName.Contains(SearchFirstName) 
                        && b.LastName.Contains(SearchLastName)
                        select b;

如果我不知道如何構建查詢 - 哪個歸檔用戶將填寫？ 也許他會為SearchLastName和SearchNumber輸入值......

Answer 1

你可以這樣做

var query = DBContext.EventDocuments;

if(!string.IsNullOrEmpty(SearchFirstName))
{
    query = query.Where(x => x.FirstName.Contains(SearchFirstName));
}
if(!string.IsNullOrEmpty(SearchLastName))
{
    query = query.Where(x => x.LastName.Contains(SearchLastName));
}

var result = query.ToList();

並根據您需要的條件構建查詢。

Answer 2

Predicate Builder是一種有效的方法。

將以下代碼放在靜態PredicateBuilder類中 ，

 public static Expression<Func<T, bool>> ContainsPredicate<T>(string memberName, string searchValue)
        {
            var parameter = Expression.Parameter(typeof(T), "m");
            var member = Expression.PropertyOrField(parameter, memberName);
            var body = Expression.Call(
                member,
                "Contains",
                Type.EmptyTypes, // no generic type arguments
                Expression.Constant(searchValue)
            );
            return Expression.Lambda<Func<T, bool>>(body, parameter);
        }

在你的cs文件中，

var filterResults = PredicateBuilder.ContainsPredicate<Employee>(columnName, searchName);

和yourLinqQuery.Where(filterResults);

供參考： Predicate Builder詳細信息

Answer 3

我建議您使用Dynamic Linq動態構造查詢。

https://weblogs.asp.net/scottgu/dynamic-linq-part-1-using-the-linq-dynamic-query-library

Answer 4

 var query = from eventDocument in DBContext.EventDocuments
                     where string.IsNullOrEmpty(firstName) || eventDocument.FirstName.Contains(firstName)
                     && string.IsNullOrEmpty(lastName) || eventDocument.LastName.Contains(lastName)
                     && string.IsNullOrEmpty(number) || eventDocument.Number.Contains(number)
                     select eventDocument;

Answer 5

以下為我工作

  var query = from b in DBContext.EventDocuments
                    where (b.FirstName.Contains(SearchFirstName) && (!string.IsNullOrEmpty(SearchFirstName))
                    && (b.LastName.Contains(SearchLastName) && (!string.IsNullOrEmpty(SearchLastName))
                    && (b.SearchNumber.Contains(SearchNumber) && (!string.IsNullOrEmpty(SearchNumber))
                   select b;

我在下面嘗試過

List<EventDocument> lsteventDoc = new List<EventDocument>() { 
            new EventDocument{ID1 ="1", ID2=2, FirstName ="", LastName="Test", Number="1"},
            new EventDocument{ID1 ="1", ID2=2, FirstName ="test", LastName="Test", Number="1"},
            new EventDocument{ID1 ="1", ID2=2, FirstName ="", LastName="", Number="1"},
        };
        string SearchFirstName = "test";
        string SearchLastName="Test";
        string SearchNumber="1";
        var query = from b in lsteventDoc
                    where (b.FirstName.Contains(SearchFirstName) && (!string.IsNullOrEmpty(SearchFirstName)))
                    && (b.LastName.Contains(SearchLastName) && (!string.IsNullOrEmpty(SearchLastName)))
                    && (b.Number.Contains(SearchNumber) && (!string.IsNullOrEmpty(SearchNumber)))
                   select b;

Answer 6

var query = from b in DBContext.EventDocuments
    where (b.FirstName.Contains(SearchFirstName) || SearchFirstName == "") 
    && (b.LastName.Contains(SearchLastName) || SearchLastName == "")
    && (b.Number.Contains(SearchNumber) || SearchNumber == "")
select b;