How to nest data from a join table in a one (or many) to many relationship in knex.js? - sql

Question

Let's say I have users, skills and user_skill tables.
How can I query so that if I have 3 users, I get 3 objects (in an array, obviously) and for each user's object there should be a nested array with all the skills?
Something like this:
{
"users": [
{
"name": "dusan",
"id": 1,
"facebook": "dusan's facebook",
"skills": [
{"name": "skill1", "id": 1}
{"name": "skill2", "id": 2}
]
},
{
"name": "jenny",
"id": 2,
"facebook": "jenny's facebook",
"skills": [
{"name": "skill1", "id": 1}
{"name": "skill2", "id": 2}
]
},
{
"name": "michael",
"id": 3,
"facebook": "michael's facebook",
"skills": [
{"name": "skill1", "id": 1}
{"name": "skill2", "id": 2}
]
},
]
}
My code:
await db("users")
.join("user_skill", "users.id", "skills.user_id")
.join("skills", "skills.id", "user_skill.id")
.select(
"users.name as name",
"users.id as id",
"skills.name as skill",
"skills.id as skill_id"
);
The above code returns a completely flat structured JSON, and I want to have skills nested inside the user object.
{
"users": [
{
"name": "dusan",
"id": 1,
"skill": "node.js",
"skill_id": 1
},
{
"name": "dusan",
"id": 1,
"skill": "php",
"skill_id": 2
},
{
"name": "dusan",
"id": 1,
"skill": "mongodb",
"skill_id": 3
},
{
"name": "jaca",
"id": 2,
"skill": "angular",
"skill_id": 4
},
{
"name": "jaca",
"id": 2,
"skill": "reactjs",
"skill_id": 5
},
]
}
I understand this is how SQL is designed, to return flat structure, but is there a way I could accomplish the nesting of related data?

Answer 1

A fellow developer has come up with this solution, so I've decided to share it in hope that someone would find it helpful:
returnedUsers = {
"users": [{
"name": "dusan",
"id": 1,
"skill": "node.js",
"skill_id": 1
},
{
"name": "dusan",
"id": 1,
"skill": "php",
"skill_id": 2
},
{
"name": "dusan",
"id": 1,
"skill": "mongodb",
"skill_id": 3
},
{
"name": "jaca",
"id": 2,
"skill": "angular",
"skill_id": 4
},
{
"name": "jaca",
"id": 2,
"skill": "reactjs",
"skill_id": 5
},
]
};
const groupBy = (array, key) =>
array.reduce((a, c) => ({
...a,
[c[key]]: [...a[c[key]] || [], c]
}), {});
const uniques = (...values) =>
Array.from(new Set([].concat(...values).filter(Boolean)));
const singularize = array =>
array.length == 1 ? array[0] : array;
const singularizedUniques = (...values) =>
singularize(uniques(...values));
const mergeCollect = array =>
array.reduce((mergedObject, curentObject) =>
Object.entries(curentObject).reduce((newObject, [k, v]) => ({
...newObject,
[k]: singularizedUniques(newObject[k], v)
}), mergedObject), {});
const groupByKey = (array, key) =>
Object.fromEntries(Object.entries(groupBy(array, key)).map(([k, v]) => [k, mergeCollect(v)]));
console.log(groupByKey(returnedUsers.users, 'id'));