可空对象必须在Linq where子句中具有值

Question

Why would a nullable int give this error using linq?

public void test(int? variableId)
{
     var date = _dbContext.Set<MyEvent>()
              .Where(x => x.Calendar.id == (variableId.HasValue ? variableId   : x.Calendar.id))
              .ToList();
}

• variableId.HasValue is false
• variableId is null

Answer 1

You should write it as (variableId.HasValue ? variableId. Value : x.Calendar.id)

Assuming variableId is null, then you have a very funny expression .Where(x => x.Calendar.id == x.Calendar.id) that means - all records. The problem with your code is that having your original where expression most likely cause client side filtering but not sql side filtering. It is better to rewrite it like:

var date = variableId.HasValue
      ?_dbContext.Set<MyEvent>().Where(x => x.Calendar.id == variableId.Value))
      :_dbContext.Set<MyEvent>();