动态查询与实体框架

Question

所以我有一个实体叫Customer。客户有name,address,gender,birthdate,city和number of kids。

我想让用户可以在这些字段上进行非常动态的过滤。例如。他可以添加一个文本域来过滤名称，然后添加另一个过滤另一个名称，然后添加另外两个文本域以在两个日期之间过滤出生日期等等...用户还可以选择过滤到日期或等于一个日期。所以事先并不知道用户想要应用多少个过滤器。

我该如何构建这种查询，最好是使用LINQ？

在此先感谢。

Answer 1

为ASP.NET MVC 4搜索动态Linq查询生成器。它是一个nuget包，允许您进行动态linq查询。

Answer 2

这将与您如何编写SQL查询类似，检查是否给出参数，然后将其作为过滤器应用。

public class Customer 
    { 
     public string Name; 
     public string Address; 
     public string City; 
     public string Gender; 
     public DateTime Birthdate; 
     public int NumberOfKids; 
    } 

    public IEnumerable<Customer> CustomerSearch(
     string partialName = null, 
     string partialAddress = null, 
     string partialCity = null, 
     string gender = null, 
     DateTime? exactBirthdate = null, 
     DateTime? startDate = null, 
     DateTime? endDate = null, 
     int? minNumberOfKids = null) 
    { 
     // Sample data 
     var customers = new [] { 
      new Customer { Name = "Jack", Birthdate = DateTime.Today.AddYears(-30), NumberOfKids = 1 }, 
      new Customer { Name = "Jill", Birthdate = DateTime.Today.AddYears(-33).AddMonths(3), NumberOfKids = 2 }, 
      new Customer { Name = "Bob", Birthdate = DateTime.Today.AddYears(-35), NumberOfKids = 3 } 
     }; 
     var query = 
      from c in customers 
      where (String.IsNullOrWhiteSpace(partialName) || c.Name.Contains(partialName)) 
       && (String.IsNullOrWhiteSpace(partialAddress) || c.Address.Contains(partialAddress)) 
       && (String.IsNullOrWhiteSpace(partialCity) || c.City.Contains(partialCity)) 
       && (String.IsNullOrWhiteSpace(gender) || c.Gender == gender) 
       && (!exactBirthdate.HasValue || c.Birthdate.Date == exactBirthdate.Value.Date) 
       && (!startDate.HasValue || !endDate.HasValue || c.Birthdate.Date >= startDate.Value.Date && c.Birthdate.Date <= endDate.Value.Date) 
       && (!minNumberOfKids.HasValue || c.NumberOfKids >= minNumberOfKids.Value) 
      select c; 
     return query; 
    } 

，并调用它是这样的：

 test.CustomerSearch("J", minNumberOfKids: 2).ToList().ForEach(c => Console.WriteLine("J and 2 kids " + c.Name)); 
     test.CustomerSearch(exactBirthdate: DateTime.Today.AddYears(-35)).ToList().ForEach(c => Console.WriteLine("exact birthdate " + c.Name)); 
     test.CustomerSearch(startDate: DateTime.Today.AddYears(-36), endDate: DateTime.Today.AddYears(-31)).ToList().ForEach(c => Console.WriteLine("birthdate between " + c.Name));