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select¶

select keeps only the fields you name, or, with -, everything but the fields you name. Less data on the wire, and nothing a screen does not need.

Only these fields

GET /api/schema/admin/mysql8/inventory/customers?select=first_name,last_name

Answer : the primary key always comes along

{
    "success": true,
    "statusCode": 200,
    "data": [
        { "customer_id": 1, "first_name": "Bob", "last_name": "Lin" },
        { "customer_id": 2, "first_name": "Alice", "last_name": "Page" }
    ]
}

Everything but these fields

GET /api/schema/admin/mysql8/inventory/customers?select=-last_update,-isActive

Body of the query APIs : a string or an object

{ "find": {}, "select": "first_name,last_name" }
{ "find": {}, "select": { "first_name": 1, "last_name": 1 } }

On MongoDB a nested field selects too : select=address.city.
Do not mix included and excluded fields in one select.
The write APIs (save, master save, update by id, replace by id, remove by id) accept select to shape the row they answer with.
Inside a deep item, select picks the fields of the related rows : deep=[{s_key:'customer_id',t_col:'orders',t_key:'customer_id',select:'order_no,total'}].
A field the group of the caller can not read never comes back, selected or not : that is the field permission of API group permission.

Arrays on MongoDB : $slice and $elemMatch¶

A field of a MongoDB document can hold an array. select takes the two operators MongoDB has to shape one, on the generated and on the schema APIs :

Operator	Example	The array comes back with
`$slice`	`{ "tags": { "$slice": 2 } }`	its first 2 items, its last 2 with `-2`
`$slice`	`{ "orders": { "$slice": [ 10, 5 ] } }`	5 items after the first 10 : `[ skip, limit ]`
`$elemMatch`	`{ "orders": { "$elemMatch": { "status": "PAID" } } }`	its first item which meets the conditions

The last 3 orders of each customer

{ "find": {}, "select": { "first_name": 1, "orders": { "$slice": -3 } } }

As a query param (JSON5)

GET /api/schema/admin/mongodb/inventory/customers?select={first_name:1,orders:{$slice:-3}}

Next to fields with 1, those fields and the array come back. Alone, $slice leaves every other field in, and $elemMatch returns the array with the id only, as MongoDB does.
The conditions of $elemMatch are the ones of find. The schema APIs convert their values to the types of the schema : { "order_id": "5" } matches the number 5, an id string an ObjectId.
$elemMatch is for an array at the top of the document. $slice cuts a nested one too : { "orders.items": { "$slice": 1 } }.
On the schema APIs $slice takes numbers only, and any other object in select selects the whole field : nothing is computed from other fields.
select of a deep item and of the write APIs takes them too.
A table of a SQL instance holds no arrays : there the field is selected as it is.

deep → sort