Loading relational data

There’s two solution for getting loading relational data

(1) RANGE based query + GET query

Let me show you example code.

export async function itemsByEndingTime(
  order: 'DESC' | 'ASC' = 'DESC',
  offset: number = 0,
  count: number = 10
): Promise<Item[]> {
  // First range-based query
  const itemIdList = await redisClient.zRange(generateItemEndingAtKey(), Date.now(), '+inf', {
    BY: 'SCORE',
    LIMIT: {
      offset: offset,
      count: count
    }
  });

  // Pipeline with two separated commands
  const results = await Promise.allSettled(itemIdList.map(itemId => redisClient.hGetAll(generateItemKey(itemId))));

  if (isExistsError(results)) {
    throw new Error("Error occurs when sorting items by ending time");
  }

  return results
    .filter(result => result.status === 'fulfilled')
    .map((item: PromiseFulfilledResult<any>, index)=> {
      return deserializeItem(itemIdList[index], item.value);
    });
}

Pros

Simple solution

Cons

This solution requires two redis operation (two network round trip)

(2) Sort

Use the SORT command for loading relational data.

When to use

• Sort data types on sets, sorted sets, lists
• Apply different sort criteria.

How to operate SORT?

-- [Requirement] Sort book name order by book's year
-- (1) 'SORT' Extract all the members from books:likes (sorted set)
-- (2) 'BY'     Take each different members and going to insert them into this template
-- good -> 1950, bad -> 1930, ok -> 1940
-- (3) 'GET' # (pound) means that insert original ID whatever the origiannl member was
-- (4) 'GET' repeat that same thing in (2) . Loop through each member and get the property (key)
-- (5) 'GET'  loop all year!
-- Return members with original ID and joined title

SORT books:likes BY books:*->year GET # GET books:*->title GET books:*->year

Original data

Sort internally with join GET

Result

No sort

Use nosnort keyword instead of arbitrary key name.

If not exist key on ‘BY’ clause, SORT operation doesn’t sort.
Just follow original data sequence.
In this situation, you could use nosort keyword

-- [No Sort] Use 'nosort' keyword
-- Apply no sort (In this example, followed by sorted set order status)
SORT books:likes BY nosort GET # GET books:*->title

Pros

Just one network round trip.
Single operation

Cons

Relatively complex query and code.