How to implement in Datomic relationships sorted by many?

Question

Datomic lacks an out-of-box function for sorting child objects in many ways, but this is a very common requirement. Googling revealed several solutions, so I wanted to describe the requirements and solutions here and rely on community comments.

Possible requirements

• R1: small numbers (N) of child objects (not sure what the small / large threshold should be)
• R2: a large number of children
• R3: single parent children
• R4: children with multiple parents
• R5: recursive children, i.e. trees stored in datomic

My specific use case is R1 + R3 + R5, which I suspect is fairly common, but I wanted to list as many as possible so that this could be a useful reference for others in the future.

Solutions

• S1: objects of nested components with the attribute “position”, for example. Datofu
• S2: add a position attribute for each child, as described using transactor fns here and in this post
• S3: linked list using the "next" attribute for each child implemented in datomic-linklist
• S4: individual wrapper objects representing edges as described in this post

Problems

Each solution has problems. Can I think:

• P1: , . "",
• P2:
• P3: , .
• P4: "position" " " , .
• P5: / ( ) -

, P2 P1 , N

, , S2. , - , , .

: - , ? R, S P , . ( ) .

A , .

Answer 1

( ), Datomic Linked List -, , fork/fix/deploy .

, .

. , 1 , . , , .

, .

Answer 2

( ).

one-to-many many-to-many parent-child:

• one-to-many , , :db/id, :my.domain/guid, :ordinal/ref .
• many-to-many , .

, latest change date/ , . , , .

, recursive pull patterns and queries. attribute on child - . separate entity, :

{:foo/bars [{:db/id 4}
            {:db/id 2}]
 :foo/bars-order [{:db/id 9 :ordinal/idx 0 :ordinal/ref {:db/id 2}}
                  {:db/id 8 :ordinal/idx 1 :ordinal/ref {:db/id 4}}]} 

: , .

, linked list vs. position values . , positional values tx-data (, 0 10 10 -, 10 ).

, - - - (parent-wrapper-child), .

:
single-parent + recursive queries= idx next .