在 Entity Framework 核心中包含集合
Include collection in Entity Framework Core
例如,我有那些实体:
public class Book
{
[Key]
public string BookId { get; set; }
public List<BookPage> Pages { get; set; }
public string Text { get; set; }
}
public class BookPage
{
[Key]
public string BookPageId { get; set; }
public PageTitle PageTitle { get; set; }
public int Number { get; set; }
}
public class PageTitle
{
[Key]
public string PageTitleId { get; set; }
public string Title { get; set; }
}
如果我只知道 BookId,我应该如何加载所有的 PageTitles?
这就是我尝试执行此操作的方式:
using (var dbContext = new BookContext())
{
var bookPages = dbContext
.Book
.Include(x => x.Pages)
.ThenInclude(x => x.Select(y => y.PageTitle))
.SingleOrDefault(x => x.BookId == "some example id")
.Pages
.Select(x => x.PageTitle)
.ToList();
}
但问题是,它会抛出异常
ArgumentException: The properties expression 'x => {from Pages y
in x select [y].PageTitle}' is not valid. The expression should represent
a property access: 't => t.MyProperty'. When specifying multiple
properties use an anonymous type: 't => new { t.MyProperty1,
t.MyProperty2 }'. Parameter name: propertyAccessExpression
怎么了,我该怎么办?
尝试直接在 ThenInclude
中访问 PageTitle
:
using (var dbContext = new BookContext())
{
var bookPages = dbContext
.Book
.Include(x => x.Pages)
.ThenInclude(y => y.PageTitle)
.SingleOrDefault(x => x.BookId == "some example id")
.Select(x => x.Pages)
.Select(x => x.PageTitle)
.ToList();
}
例如,我有那些实体:
public class Book
{
[Key]
public string BookId { get; set; }
public List<BookPage> Pages { get; set; }
public string Text { get; set; }
}
public class BookPage
{
[Key]
public string BookPageId { get; set; }
public PageTitle PageTitle { get; set; }
public int Number { get; set; }
}
public class PageTitle
{
[Key]
public string PageTitleId { get; set; }
public string Title { get; set; }
}
如果我只知道 BookId,我应该如何加载所有的 PageTitles?
这就是我尝试执行此操作的方式:
using (var dbContext = new BookContext())
{
var bookPages = dbContext
.Book
.Include(x => x.Pages)
.ThenInclude(x => x.Select(y => y.PageTitle))
.SingleOrDefault(x => x.BookId == "some example id")
.Pages
.Select(x => x.PageTitle)
.ToList();
}
但问题是,它会抛出异常
ArgumentException: The properties expression 'x => {from Pages y in x select [y].PageTitle}' is not valid. The expression should represent a property access: 't => t.MyProperty'. When specifying multiple properties use an anonymous type: 't => new { t.MyProperty1, t.MyProperty2 }'. Parameter name: propertyAccessExpression
怎么了,我该怎么办?
尝试直接在 ThenInclude
中访问 PageTitle
:
using (var dbContext = new BookContext())
{
var bookPages = dbContext
.Book
.Include(x => x.Pages)
.ThenInclude(y => y.PageTitle)
.SingleOrDefault(x => x.BookId == "some example id")
.Select(x => x.Pages)
.Select(x => x.PageTitle)
.ToList();
}