joinTo
fun <T, A : Appendable> MongoIterable<T>.joinTo(buffer: A, separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: (T) -> CharSequence? = null): A
Appends the string from all the elements separated using separator and using the given prefix and postfix if supplied.
If the collection could be huge, you can specify a non-negative value of limit, in which case only the first limit elements will be appended, followed by the truncated string (which defaults to "...").