javascript - Filter array of objects to a single matching object in mongodb/meteor -

i have query looks so:

var writer = writers.findone({   _id: writerid,   books: {     $elemmatch: {       id: books.findone({ slug: bookslug })._id     }   } }); 

however, return full list of classes in query.

{   name: "h.p. lovecraft",   books: [{     id: "1234",     slug: "at-the-mountains-of-madness"   }, {     id: "5678",     slug: "herbert-west-reanimator"   }] } 

would there way eliminate information except 1 item in list want , make object? say, want final result be:

{   name: "h.p lovecraft",   book: {     id: "1234",     slug: "herbert-west-reanimator"   } } 

how done in meteor mongodb?

one approach take use $elemmatch projection operator findone() query. document _id equal writerid, $elemmatch projection returns first matching element array:

var bookid = books.findone({ slug: bookslug })._id,     writer = writers.findone({ _id: writerid },                              { books: { $elemmatch: { id: bookid } },                                 _id: 0,                                name: 1                              }     ); 

another approach use underscore library's _.find() method return specific array element:

var bookid = books.findone({ slug: bookslug })._id,     writer = writers.findone({         _id: writerid,         books: {             $elemmatch: {                 id: bookid             }         }     }),     book = _.find(writer.books, function(book) {return book.id === bookid});