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select¶

select keeps only the columns you name. With -, it keeps everything but the columns you name. The answer is smaller, and holds only what your screen needs.

In short

?select=first_name,last_name : only these columns. ?select=-password : all but this one.
With a schema, the primary key always comes along.
Columns the groups of the caller may not read never come back.

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 works too : select=address.city.
Do not mix kept and left-out columns. If you do, only the left-out ones count : select=first_name,-pincode returns every column but pincode.
On a schema API, a column the schema does not have stops the call : Unable to find [nick_name] columns in schema of [mysql8 → inventory → customers].
The write APIs (save, master save, update by id, replace by id, remove by id) take select too. It shapes the row they answer.
In a deep item, select picks the columns of the related rows : deep=[{s_key:'customer_id',t_col:'orders',t_key:'customer_id',select:'order_no,total'}].
A column the groups of the caller may not read never comes back, selected or not. See the column permissions 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