如何使用传递的字符串参数从控制器编写 MVC Entity Framework select 查询？

Question

我在 MVC 中创建了一个搜索工具。用户将 searchTerm 字符串键入搜索框和 selects 选项以从 2 个下拉 select 列表中进行搜索。在第一个列表中，用户 selects "Fuzzy" 或 "Literal" 用于搜索类型，在第二个列表中，用户可以 select 搜索特定字段，specField。单击搜索按钮后，3 个字符串值将传递给控制器。
我正在尝试编写一个 "if" 语句，该语句根据传入控制器的这 3 个字符串值查询 Entity Framework 数据库模型。如何编写使用这些值的查询？这就是我所拥有的。我知道查询没有写正确：

 Public PartialViewResult _Search(string searchTerm, string specField, string searchType)
 {
      //This works to populate the table with the entire DB 
      _db = new IntegrationDBEntities();
      var request = (from r in _db.Requests
                     select r).ToList();

     //These two are not correct and I need help writing these
     if (searchType == "Fuzzy" && searchTerm != "" && specField != "None")
     {
          request = (from r in _db.Requests
                          where r.(specField).Contains(searchTerm)
                          select r).ToList();
     }
     if (searchType == "Literal" && searchTerm != "" && specField == "None")
     {
          request = (from r in _db.Requests
                         where r.Equals(searchTerm)
                         select r).ToList();
     }
     ViewData.Model = request;
     Return partialView();
 }

Answer 1

希望这没有错误：

ParameterExpression pe = Expression.Parameter(typeof(Request), "Request");
Expression property = Expression.Property(pe, specField);
Expression predicate = null;
Expression srch = Expression.Constant(searchTerm, typeof(string));
if(searchType == "Fuzzy")
{
    MethodInfo contains = typeof(string).GetMethod("Contains", new Type[] { typeof(string) });
    predicate = Expression.Call(property, contains, srch);
}
else
{
    predicate = Expression.Equal(property, srch);
}

MethodCallExpression where = Expression.Call(
    typeof(Queryable),
    "Where",
    new Type[] { _db.Requests.ElementType },
    _db.Requests.Expression,
    Expression.Lambda<Func<Request, bool>>(predicate, new ParameterExpression[] { pe }));

IQueryable<Request> result = _db.Requests.Provider.CreateQuery<Request>(where);

var list = result.ToList();

如果您有任何问题，请告诉我

Answer 2

我不是 100% 确定你的 Request 对象是什么样子的，但我会使用 PredicateBuilder。这是您的搜索功能的示例。

IQueryable<Request> SearchRequests (string searchTerm, string specField, string searchType)
{
    var predicate = PredicateBuilder.False<Request>();

    //These two are not correct and I need help writing these
    if (searchType == "Fuzzy" && searchTerm != "" && specField != "None")
    {
        predicate = predicate.Or (r => r.(specField).Contains(searchTerm));
    }
    if (searchType == "Literal" && searchTerm != "" && specField == "None")
    {
        predicate = predicate.Or (r => r.Equals(searchTerm));
    }

    return new IntegrationDBEntities()
                  .Requests
                  .AsExpandable()
                  .Where(predicate);
}

那么您的方法可能如下所示：

Public PartialViewResult _Search(string searchTerm, string specField, string searchType)
 {
     ViewData.Model = SearchRequests(searchTerm, specField, searchType).ToList();
     Return partialView();
 }

更新：我添加了来自 LinqPad 的工作示例。您需要稍微修改它才能使其适用于 EntityFramework.

void Main()
{
    var results = SearchRequests("Fuzzy", "later").ToList();
    results.Dump();

    var results2 = SearchRequests("Literal", "Test me now").ToList();
    results2.Dump();
}

// Define other methods and classes here
public class Request
{
    public int Id {get;set;}
    public string SearchTerm {get;set;}
}

public IQueryable<Request> LoadData()
{
    var list = new List<Request>();
    list.Add(new Request {Id = 1, SearchTerm = "Test me now"});
    list.Add(new Request {Id = 2, SearchTerm = "Test me later"});
    list.Add(new Request {Id = 3, SearchTerm = "Test me maybe"});
    list.Add(new Request {Id = 4, SearchTerm = "Test me now"});
    list.Add(new Request {Id = 5, SearchTerm = "Test me later or never"});
    list.Add(new Request {Id = 6, SearchTerm = "Test me maybe or today"});

    return list.AsQueryable();
}

public IQueryable<Request> SearchRequests (string searchType, string searchTerm)
{
    var data = LoadData();
    var predicate = PredicateBuilder.False<Request>();
    //These two are not correct and I need help writing these
    if (searchType == "Fuzzy")
    {
        predicate = predicate.Or(r => r.SearchTerm.Contains(searchTerm));
    }
    if (searchType == "Literal")
    {
        predicate = predicate.Or (r => r.SearchTerm.Equals(searchTerm));
    }

    return data.Where(predicate);
}

public static class PredicateBuilder
{
    public static Expression<Func<T, bool>> True<T> ()  { return f => true;  }
    public static Expression<Func<T, bool>> False<T> () { return f => false; }

    public static Expression<Func<T, bool>> Or<T> (this Expression<Func<T, bool>> expr1,
                                                        Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
        return Expression.Lambda<Func<T, bool>>
            (Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
    }

    public static Expression<Func<T, bool>> And<T> (this Expression<Func<T, bool>> expr1,
                                                        Expression<Func<T, bool>> expr2)
    {
        var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast<Expression> ());
        return Expression.Lambda<Func<T, bool>>
            (Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
    }
}

首次搜索结果：

Id  SearchTerm
2   Test me later
5   Test me later or never

第二次搜索结果：

Id  SearchTerm
1   Test me now
4   Test me now

如何使用传递的字符串参数从控制器编写 MVC Entity Framework select 查询？

How do I write an MVC Entity Framework select query from the controller using passed string arguments?

c#

linq

viewdata

entity-framework

asp.net-mvc-4