ASP.NET搜索表單 - 動態Linq to SQL？

Question

我有一個搜索表單，允許用戶以幾種不同的方式搜索幾個不同的字段。這是我的代碼的一個例子。

var claims = from c in db.Claims select c; 

switch (ddlSearchField.Text) 
{ 
    case "StartsWith": 
     claims = claims.Where(c => c.companyFileID.StartsWith(txtSearchBox.Text)); 
     break; 

    case "Equals": 
     claims = claims.Where(c => c.companyFileID == txtSearchBox.Text); 
     break; 

    case "Contains": 
     claims = claims.Where(c => c.companyFileID.Contains(txtSearchBox.Text)); 
     break; 
} 

我有十個不同的領域，用戶可以搜索，所以我外面的開關語句是相當大的。必須有一個更優雅的方式來完成這一點。

Answer 1

您可以通過創建重構代碼的某些部分一種擴展方法。類似的東西：

static class QueryableExtensions 
{ 
    private static MethodInfo StringContainsMethod; 
    private static MethodInfo StringStartsWithMethod; 

    static QueryableExtensions() 
    { 
     Type[] singleStringParam = new[] {typeof(string)}; 
     StringContainsMethod = typeof(string).GetMethod("Contains", singleStringParam); 
     StringStartsWithMethod = typeof(string).GetMethod("StartsWith", singleStringParam); 
    } 

    public static IQueryable<T> AppendTextFilter<T>(this IQueryable<T> queryable, Expression<Func<T, string>> memberSelector, string condition, string value) 
    { 
     Expression expression = null; 
     switch (condition) 
     { 
      case "StartsWith": 
       expression = Expression.Call(
           memberSelector.Body, 
           StringStartsWithMethod, 
           Expression.Constant(value)); 
       break; 

      case "Equals": 
       expression = Expression.Equal(
           memberSelector.Body, 
           Expression.Constant(value)); 
       break; 

      case "Contains": 
       expression = Expression.Call(
           memberSelector.Body, 
           StringContainsMethod, 
           Expression.Constant(value)); 
       break; 

      default: 
       throw new NotSupportedException(string.Format("'{0}' is not a supported condition", condition)); 
     } 

     var lambda = Expression.Lambda<Func<T, bool>>(
         expression, 
         memberSelector.Parameters); 
     return queryable.Where(lambda); 
    } 
} 

然後，您可以使用它像：

var claims = db.Claims 
      .AppendTextFilter(c => c.companyFileID, ddlSearchField.Text, txtSearchBox.Text) 
      .AppendTextFilter(c => c.someOtherProperty, ddlOtherSearchField.Text, txtOtherSearchBox.Text) 
      ...; 

Answer 2

你試過動態LINQ嗎？它允許您構建類似於SQL WHERE子句的基於字符串的查詢語句。

http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

Answer 3

你可以讓你的可能謂詞的詞典：

Dictionary<string, Func<string, Expression<Func<Claim, bool>>>> map = new Dictionary<string, Func<string, Expression<Func<Claim, bool>>>>() { 
    { "StartsWith", t => c => c.companyFileID.StartsWith(t) }, 
    { "Equals",  t => c => c.companyFileID == t }, 
    { "Contains", t => c => c.companyFileID.Contains(t) } 
}; 

哪位能像這樣被使用：

var search = ddlSearchField.Text; 
var text = txtSearchBox.Text; 

var claims = from c in db.Claims select c; 

Func<string, Expression<Func<Claim, bool>>> predicate = null; 
if(dict.TryGetValue(search, out predicate)) 
    claims = claims.Where(predicate(text));