实体框架：条件过滤器 [英] entity framework: conditional filter

问题描述

假设我有Customers表，我想通过以下方式过滤：

• 国家：美国，英国，加拿大


• 收入：全部，低，高，中


• 年龄：所有，青少年，成人
ul>



如果我必须为此过滤器构建一个SQL字符串，它将是这样：

  if（Country！=All）sql + =country =+ Country 
 if（Income！=All）sql + =and income =+ Income 
 if（Age！=All）sql + =and age =+ Age; 
  

因此，基本上，用户可以筛选一些，但不是必要的所有字段。




$ b

谢谢！

解决方案

您可以通过这种方式包含条件参数：

  return Customers.Where b $ b customer => 
 customer.Name == Name& 
（Age ==All|| customer.Age == Age）&& 
 Income ==All|| customer.Income == Income）&& 
（Country ==All|| customer.Country == Country）
）.ToList（）; 
  

如果某些条件为真（例如country等于 All ），那么所有参数条件变为true，并且此参数不过滤结果。




Let's say I have Customers table and I want to filter it by the following:

• Country: All, US, UK, Canada
• Income: All, low, high, medium
• Age:All, teenager, adult, senior

if I had to build an SQL string for this filter, it would be something like this:

if (Country != "All") sql += "country = " + Country
if (Income != "All") sql += "and income = " + Income
if (Age != "All") sql += "and age = " + Age;

So, basically, the user can filter by some, but not necessary all fields.

How do you do this using Entity Framework ?

Thanks !

解决方案

You can include conditional parameter this way:

return Customers.Where(
                customer =>
                customer.Name == Name &&
                (Age == "All" || customer.Age == Age) &&
                (Income == "All" || customer.Income == Income) &&
                (Country == "All" || customer.Country == Country)
                ).ToList();

If some condition is true (e.g. country is equal to All), then all parameter condition becomes true, and this parameter does not filter result.

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