Flappy search bar: Implementing search

I am relatively new to flutter app development and therefore I am having issues implementing search on my app from the firestore cloudstore db. Currently I have the following code:

  Widget build(BuildContext context) {

    Future<DocumentSnapshot> search(String search) async {
      List<DocumentSnapshot> bookList = (await Firestore.instance
            .collection("book_data")
            .where("booksearch", arrayContains: search)
            .getDocuments())
          .documents;

      return List.generate(bookList.length, (int index) {
        return bookList;
      });
    }

    return Scaffold(
      backgroundColor: Colors.black,
      body: SafeArea(
        child: Padding(
          padding: EdgeInsets.fromLTRB(15, 20, 15, 15),
          child: SearchBar<List<DocumentSnapshot>>(
            crossAxisCount: 1,
            hintText: 'Search',
            cancellationWidget: Icon(
              Icons.close,
              color: Colors.grey,
            ) ,
            searchBarStyle: SearchBarStyle(
              padding: EdgeInsets.all(2),
              borderRadius: BorderRadius.circular(10),
            ),
            iconActiveColor: Colors.white,
            emptyWidget: Center(
              child: Text("No results found! :(",
                style: TextStyle(
                    color: Colors.grey,
                    fontSize: 12.0,
                    fontWeight: FontWeight.normal
                ),
              ),
            ),
            icon: Padding(
              padding: const EdgeInsets.fromLTRB(12, 0, 0, 0),
              child: Icon(
                Icons.search,
                color: Colors.grey,
              ),
            ),
            textStyle: TextStyle(
                color: Colors.white
            ),
            onSearch: search,
            onItemFound: ( bookList, int index) {
              return ListTile(
                title: Text(
                  bookList.bookname,
                  style: TextStyle(
                      color: Colors.white
                  ),
                ),
                subtitle: Text(
                  book.author,
                  style: TextStyle(
                      color: Colors.white
                  ),
                ),
              );
            },
          ),
        ),
      ) ,
    );
  }

I actually want to compare the search query with the array having the label "booksearch" present in the "book_data" collection irrespective of which document it is in. Kindly help me with this.