c# - Mongodb In Query 对每条记录都有限制

Question

我有一个 id 的 authorIds=["1","2",3","4"] 数组。我有另一个数组保存对 authorId 的引用。例如:

book=[
{
      bookId:"abcd",
      authorId:"1"
},
{
      bookId:"def",
      authorId:"1"
}
{
      bookId:"ghi",
      authorId:"2"
}
{
      bookId:"kjl",
      authorId:"1"
}
];

现在我想使用 In 查询 (mongodb C# drvier)，但想将每位作者的书籍数量限制为 5 本书。谁能告诉我该怎么做。

Answer 1

您可以使用Limit 选项来实现这一点:

var builder = Builders<Book>.Filter;
FilterDefinition<Book> filter = builder.In((b => b.authorId), authorIds);
var find = products.Find(filter);
find.Options.Limit = 5;

var bookList = find.ToListAsync().Result;

您还可以将 SortBy 组合到此:

var builder = Builders<Book>.Filter;
FilterDefinition<Book> filter = builder.In((b => b.authorId), authorIds);
var sorted = products.Find(filter).SortBy(b => b.bookId);
sorted.Options.Limit = 5;

var bookList = sorted.ToListAsync().Result;