Using arrays items in JSON Schema - json

Question

I am very new to JSON Schema. I have a requirement in a array few items are mandatory and few are optional. Each item is having different validation rules. All the items may not come is sequence order. I have to create this schema only in draft04 version.
My JSON message is as below.
{
"Event": {
"AttributeList": [
{
"Attribute": {
"name": "OrderID",
"value": "String"
}
},
{
"Attribute": {
"name": "txnid",
"value": "Strinnkjnjknlg"
}
},
{
"Attribute": {
"name": "Appid",
"value": "Stg"
}
},
{
"Attribute": {
"name": "txnswitch",
"value": "false"
}
}
]
}
}
I have to build a JSON schema where Attributes with the below conditions:
The items(Attribute) under the Attribute list can have both mandatory and optional which is not working.Here "name" Appid and OrderID are mandatory and rest of them are optional ones.
The items(Attribute) can be any sequence/order.
Items shouldn't be repeated.
I have written the below schema but couldn't achieve all the conditions.
JSON Schema is as follows
{
"$schema": "http://json-schema.org/draft-04/schema#",
"type": "object",
"properties": {
"Event": {
"type": "object",
"properties": {
"AttributeList": {
"type": "array",
"uniqueItems": true,
"items": {
"allOf": [
{
"type": "object",
"properties": {
"Attribute": {
"type": "object",
"properties": {
"name": {
"type": "string",
"enum": [
"OrderID"
]
},
"value": {
"type": "string",
"maxLength": 16
}
},
"required": [
"name",
"value"
],
"optional": false
}
},
"required": [
"Attribute"
],
"optional": false
},
{
"type": "object",
"properties": {
"Attribute": {
"type": "object",
"properties": {
"name": {
"type": "string",
"enum": [
"txnid"
]
},
"value": {
"type": "string",
"maxLength": 35
}
},
"required": [
"name",
"value"
],
"optional": true
}
},
"required": [
"Attribute"
],
"optional": true
},
{
"type": "object",
"properties": {
"Attribute": {
"type": "object",
"properties": {
"name": {
"type": "string",
"enum": [
"Appid"
]
},
"value": {
"type": "string",
"maxLength": 8
}
},
"required": [
"name",
"value"
],
"optional": false
}
},
"required": [
"Attribute"
],
"optional": false
},
{
"type": "object",
"properties": {
"Attribute": {
"type": "object",
"properties": {
"name": {
"type": "string",
"enum": [
"txnswitch"
]
},
"value": {
"type": "string",
"maxLength": 28
}
},
"required": [
"name",
"value"
],
"optional": true
}
},
"required": [
"Attribute"
],
"optional": true
}
]
}
}
},
"required": [
"AttributeList"
]
}
},
"required": [
"Event"
]
}
This schema doesn't work as expected.

Answer 1

Your schema isn't working because prefixItems isn't supported with draft4 (which is what your $schema keyword indicates), plus the schema under prefixItems will only be applied to the first item, not all items.
You can achieve what you need with contains combined with minContains and maxContains. For the mandatory items, use minContains: 1 and for the optional ones, use minContains: 0. You can set maxContains: 1 for both of these to ensure each item type can't appear twice.
https://json-schema.org/understanding-json-schema/reference/array.html#contains
You'll need an evaluator that supports at least draft2019-09 for minContains and maxContains.