[英]How do you filter an in memory list dynamically using linq?
Wondering what is the best approach to filter an in memory list dynamically. 想知道什么是动态过滤内存列表的最佳方法。
Lets suppose I have in memory List and I need to write a find that filters the in memoryList based on the criteria. 让我们假设我在内存列表中,我需要编写一个基于条件过滤内存列表中的内容。 Obviously if a value is null or empty do use it.
显然,如果值是null或为空,请使用它。 How do you build the predicate.
您如何建立谓词。 I have looked at the predicateBuilder but not sure how to use it.
我看过predicateBuilder,但不确定如何使用它。
See code below 见下面的代码
public class CustomerService
{
private IEnumerable<Customer> customersInMemoryAlready;
public CustomerService()
{
customersInMemoryAlready = new List<Customer>();//Pretend we have fetched 200 customers here
}
public IEnumerable<Customer> Find(Criteria criteria)
{
IEnumerable<Customer> results = GetInMemoryCustomers();
//Now filter based on criteria How would you do it
if(!string.IsNullOrEmpty(criteria.Surname))
{
//?
}
if (!criteria.StartDate.HasValue && !criteria.EndDate.HasValue)
{
//?Get all dateOfBirth between StartDate and EnDate
}
return results;
}
private IEnumerable<Customer> GetInMemoryCustomers()
{
return customersInMemoryAlready;
}
}
public class Customer
{
public string Firstname { get; set; }
public string Surname { get; set; }
public DateTime?DateOfBirth { get; set; }
public string City { get; set; }
}
public class Criteria
{
public string Firstname { get; set; }
public string Surname { get; set; }
public DateTime?StartDate { get; set; }
public DateTime? EndDate { get; set; }
public string City { get; set; }
}
Any suggestions? 有什么建议么? Thanks
谢谢
Sure, you just use Where
: 当然,您只需使用
Where
:
public IEnumerable<Customer> Find(Criteria criteria)
{
IEnumerable<Customer> results = GetInMemoryCustomers();
//Now filter based on criteria How would you do it
if(!string.IsNullOrEmpty(criteria.Surname))
{
results = results.Where(c => c.Surname == criteria.Surname);
}
if (criteria.StartDate.HasValue && criteria.EndDate.HasValue)
{
DateTime start = criteria.StartDate.Value;
DateTime end = criteria.EndDate.Value;
results = results.Where(c => c.DateOfBirth != null &&
c.DateOfBirth.Value >= start &&
c.DateOfBirth.Value < end);
}
return results;
}
EDIT: You can use the lifted operators for DateTime?
编辑:您可以为
DateTime?
使用解除运算符DateTime?
if you want to here: 如果您想在这里:
if (criteria.StartDate.HasValue && criteria.EndDate.HasValue)
{
results = results.Where(c => c.DateOfBirth != null &&
c.DateOfBirth >= criteria.StartDate &&
c.DateOfBirth < criteria.EndDate);
}
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