[英]Filter with multiple derived classes with Code-first Entity Framework
Lets say I have a User
with 2 derived entities Student
, Teacher
. 假设我有一个带有2个派生实体的
User
Student
, Teacher
。 I used the TPH method, so I actually have no property at all in my classes to tell me who is a teacher or not. 我使用了TPH方法,所以在课堂上我根本没有任何属性可以告诉我谁是老师。
I have 2 booleans that should allow me to load either student or teacher such as this: 我有2个布尔应该允许我加载学生或老师,如下所示:
//IQueryable<User>
var query = userRepository.GetUsers();
//Type filtering
if (searchModel.IsStudent)
{
query = query.OfType<Student>();
}
if (searchModel.IsTeacher)
{
query = query.OfType<Teacher>();
}
When this tries to evaluate, I get this error when both are true: 当这个尝试评估时,当两者都为真时我得到这个错误:
DbIsOfExpression requires an expression argument with a polymorphic result type that is compatible with the type argument.
I already looked at some answers here on SO but they are geared towards 1 type of filtering. 我已经在SO上查看了一些答案,但它们适用于一种类型的过滤。
I would then like to do something like this (rough coding): 我想做这样的事情(粗略编码):
if(query.ToList().FirstOrDefault() is Student)
{
print "student";
}
The mapping: 映射:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<User>()
.Map<Teacher>(m => m.Requires("UserType").HasValue("Teach"))
.Map<Student>(m => m.Requires("UserType").HasValue("Stu"))
.Map<Staff>(m => m.Requires("UserType").HasValue("Staff"));
}
Try this one. 试试这个吧。 It works at least for EF 5.
它至少适用于EF 5。
IQueryable<User> Filter(this IQueryable<User> query,
bool includeTeacher, bool includeStudent)
{
return query.Where(x => includeTeacher && x is Teacher
|| includeStudent && x is Student);
}
This is ugly but it will work for what you need: 这很难看,但它可以满足您的需求:
if (searchModel.IsStudent && searchModel.IsTeacher)
{
var result = context.Users.OfType<Teacher>()
.Cast<User>()
.Union(context.Users.OfType<Student>());
}
And It will run on one query!! 它将在一个查询上运行!! :)
:)
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