Commits on Jun 6, 2023

1. feat: Client side in-memory joins …

   API:
   
   First, join object need to be created, which specifies collections and
   join condition:
   ```
   join := tigris.GetJoin[LeftCollModel, RightCollModel](db, "{left field}", "{right field}", [options])
   ```
   This creates a join between LeftCollModel and RightCollModel on
   equality of `{left field}` to `{right field}`.
   
   Created object then can be used to issue one or multiple read requests:
   
   ```
   it, err := join.Read(ctx, filter.Eq("Field1", 1))
   ```
   
   filter condition of read API is applied to the left table.
   Iterator then returns of the rows matching the condition along with the
   corresponding rows from the right table, which satisfies the join
   condition.
   
   var l LeftCollModel
   var r []*RightCollModel
   
   for it.Next(&l, &r) {
     fmt.Printf("l=%v r=%v\n", l, r)
   }
   
   By default the documents which doesn't have matching documents in the right
   table returned in the results. These results can be skipped by providing
   `&JoinOptions{Type: tigris.InnerJoin}` option to GetJoin API.
   
   It is not required for the left field values or right field values to be unique.
   
   The value of the array fields are matched as is by default, by using
   `&JoinOptions{ArrayUnroll: true}` option individual array items can be
   matched in the right table.
   
   Implementation details:
   
   First request is issued to the left table with filter provided to Read API.
   Result is read into memory and request is prepared for the right table.
   Which will have the following filter `filter.Or(filter.Eq("{right field}", {left field value fetched by left query}), ...)`.
   
   Result from the first query is put in the map with {left field} value as the key,
   while reading the result from second query we append it to the corresponding map bucket.
   
   So as merge is done in the memory joins should be used for relatively small
   result sets only.

   

   efirs committed Jun 6, 2023
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