First things first: what do you want to achieve with following schema definition?
"first" : [ { ...schema... } ]
As to your problem statement, I am not sure, what you want to achieve:
Schema that allows first array item to be an object with 4 keys, while all other items should have 5 keys?
Schema, that allows only array items=object with 5 keys and will reject a JSON, which does have 4 keys in first item
Could you please rephrase your question to make it more clear? I did some solution basing on assumptions, but it would be good if you could confirm my understanding.
Required reading
Please read first through:
http://json-schema.org/latest/json-schema-validation.html#rfc.section.6.4.1
If "items" is an array of schemas, validation succeeds if each element
of the instance validates against the schema at the same position, if
any.
plus https://stackoverflow.com/a/52758108/2811843 on above topic
https://json-schema.org/understanding-json-schema/reference/array.html#length
https://json-schema.org/understanding-json-schema/reference/array.html#tuple-validation
and https://json-schema.org/understanding-json-schema/reference/array.html in general
as well as
https://json-schema.org/understanding-json-schema/reference/object.html#property-names
https://json-schema.org/understanding-json-schema/reference/object.html#size
and https://json-schema.org/understanding-json-schema/reference/object.html in general.
Possible solution
After looking at sample schema I will rephrase problem statement making some wild assumptions you want a schema, that allows an array of items, where item = object. First item could have 4 keys, while all other items must have 5 keys.
I need a JSON schema that will describe an array of objects, where
first object always has 4 keys/properties, while all remaining objects
do have 5 keys/properties.
Additionally, there is always at least first item in array (containing 4 keys) and there can be up to X other
objects (containing 5 keys) in array.
Go for Tuple-typing and array of objects. Thus you might exactly check that first item (object) has exactly 4 properties and define the schema for the rest of them.
First, full working schema (with comments inside). The "examples" section contains examples of arrays to illustrate the logic, only last 3 will be valid against schema.
{
"$schema": "http://json-schema.org/draft-07/schema#",
"type": "array",
"$comment" : "This is an array, where first item must be an object with at least 4 properties and one property named \"state\" and can contain minimum 1 and maximum of 3 items",
"minItems" : 1,
"maxItems" : 3,
"items": [
{
"type": "object",
"minProperties" : 4,
"required" : ["state"],
}
],
"additionalItems" : {
"$comment" : "Any additional item in this array must be an object with at least 5 keys and two of them must be \"state\" and \"zip\".",
"type" : "object",
"minProperties" : 5,
"required" : ["state", "zip"],
},
"examples" : [
[
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
},
{},
{}
],
[
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "12345"
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
}
],
[
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "12345"
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "54321"
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "54321"
}
],
[],
[
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "12345"
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "54321"
},
],
[
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
},
],
[
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
},
{
"key1" : "1",
"key2" : "2",
"key3" : "3",
"state" : "some state",
"zip" : "12345"
},
]
]
}
So, step by step:
"type": "array",
"minItems" : 1,
"maxItems" : 3,
an JSON which is an array with minimum 1 item, maximum 3 items, will be ok. If you don't define "minItems" value, the empty array would pass validation against schema.
"items": [
{
"type": "object",
"minProperties" : 4,
"required" : ["state"],
}
],
This is the Tuple magic - a finite, ordered list of elements (sequence). Yep, maths has it's saying. By using "items" : [ ... ] instead of { ... } you fall into quoted above section of JSON Schema Validation spec (http://json-schema.org/latest/json-schema-validation.html#rfc.section.6.4.1 ).
Above basically says: This is an array, where first item must be an object with at least 4 keys and one of those keys must be "state".
Ok, last but not least:
"additionalItems" : {
"$comment" : "Any additional item in this array must be an object with at least 5 keys and two of them must be \"state\" and \"zip\".",
"type" : "object",
"minProperties" : 5,
"required" : ["state", "zip"],
}
By this I said:
in this array (which must have first item an object with 4 keys and one of those keys is "state" and oh, by the way, an array must have at least 1 item and tops 3 items) you can have additional items on top of the the ones already defined in "items" section. Each such additional item must be an object with at least 5 keys, out of which two must be "state" and "zip".
Does it solve your issue?
