[英]Load child object records with filter condition in Entity Framework
[英]Filter child records using Entity Framework
我有兩個類Author
和Book
有關系:
public class Author
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Book> Books { get; set; }
}
public class Book
{
public int Id { get; set; }
public int AuthorId { get; set; }
public string BookName { get; set; }
}
DbContext
:
public class LibraryDBContext : DbContext
{
public DbSet<Author> Authors { get; set; }
public DbSet<Book> Books { get; set; }
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer(@"Server=.\SQLEXPRESS;Database=SchoolDB;Trusted_Connection=True;");
}
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<Author>()
.HasMany(obj => obj.Books)
.WithOne()
.HasForeignKey(obj => obj.AuthorId)
.OnDelete(DeleteBehavior.Cascade)
.IsRequired();
}
}
編寫邏輯的主要方法:
class Program
{
static void Main(string[] args)
{
var book1 = new Book() { AuthorId = 1, BookName = "a" };
var book2 = new Book() { AuthorId = 1, BookName = "b" };
var book3 = new Book() { AuthorId = 1, BookName = "c" };
var author = new Author() { Name ="a" };
var mydbcontext = new LibraryDBContext();
mydbcontext.Add(author);
mydbcontext.Add(book1);
mydbcontext.Add(book2);
mydbcontext.Add(book3);
mydbcontext.SaveChanges();
// Here I am trying to get Author 1 with BookName b
var result = mydbcontext.Authors
.Include(d => d.Books)
.Where(d => d.Id == 1 &&
d.Books.Any(b => b.BookName.Equals("b")))
.AsNoTracking()
.ToList();
Console.WriteLine(JsonConvert.SerializeObject(result));
}
}
輸出:即使我過濾了BookName b
我也從Book
獲取所有記錄
[
{
"Id": 1,
"Name": "a",
"Books": [
{
"Id": 1,
"AuthorId": 1,
"BookName": "a"
},
{
"Id": 2,
"AuthorId": 1,
"BookName": "b"
},
{
"Id": 3,
"AuthorId": 1,
"BookName": "c"
}
]
}
]
為什么所有的書都返回,而不僅僅是BookName = b
?
.Where(d => d.Id == 1 && d.Books.Any(b=>b.BookName.Equals("b")))
上述條件檢查Author Id == 1
以及Author Id == 1
任何書籍是否名為b
。 它不會按作者過濾書籍,作者具有所需的名稱。
對於 Author Author ID == 1
Author 也是如此,因為他的 3 本書之一具有所需的名稱並且條件得到滿足。
你需要的是
mydbcontext.Books.Where(d => d.AuthorId== 1 && d.BookName.Equals("b"))
以上將過濾具有AuthorId=1
和BookName==b
的書籍
根據評論更新
要包含作者詳細信息,您可以將查詢修改為
var result = mydbcontext.Authors
.Include(d => d.Books)
.Where(d => d.AuthorId== 1)
.Select(x=>
new Author
{
Id=x.Id,
Name=x.Name,
Books = x.Where(c=>c.BookName.Equals("b"))
});
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