Mongo db In Query with limit for each record

Question

I have an array of id's authorIds=["1","2",3","4"]. I have another array that holds the reference to the authorIds. ex:

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

now i would like to use the In query (mongodb C# drvier) but want to restrict the number of books to 5 for each author. Can someone tell me how to do this.

Possible duplicate of limit and sort each group by in mongoDB using aggregation — Blakes Seven
– Blakes Seven, Commented Nov 11, 2015 at 6:10

jhmt · Accepted Answer · 2015-11-13 22:34:38Z

1

You can use Limit option to achieve this:

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;

you can also combine SortBy to this:

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;

answered Nov 13, 2015 at 22:34

jhmt

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