uniqueItems : Boolean
uniqueItems
BooleanIf this keyword is set to the boolean value true, the instance validates successfully if all of its elements are unique.
| Value |
This keyword must be set to a boolean value
Hint: Use the jsonschema metaschema command to catch keywords set to invalid values
|
|---|---|
| Kind | Assertion |
| Applies To | Array |
| Base Dialect | 2020-12 |
| Changed In | None |
| Introduced In | Draft 2 |
| Vocabulary | Validation |
| Specification | https://json-schema.org/draft/2020-12/json-schema-validation.html#section-6.4.3 |
| Metaschema | https://json-schema.org/draft/2020-12/meta/validation |
| Official Tests | draft2020-12/uniqueItems.json |
| Default |
false
|
| Annotation | None |
| Affected By | None |
| Affects | None |
| Also See |
|
When set to true, the uniqueItems keyword restricts array instances to
items that only occur once in the array. Note that empty arrays and arrays that
consist of a single item satisfy uniqueness by definition.
Common Pitfall
Keep in mind that depending on the size and complexity of arrays, this keyword may introduce significant validation overhead. The paper JSON: data model, query languages and schema specification also noted how the presence of this keyword can negatively impact satisfiability analysis of schemas.
Digging Deeper
While the official vocabularies do not offer a way to
ensure uniqueness of array items based a given key, the
json-everything project defines a third-party
Extended Validation of
Arrays vocabulary
that introduces a
uniqueKeys
keyword for this purpose. However, keep in mind that third-party vocabularies
are often not widely supported by implementations.
Remember that JSON Schema is a constraint-driven language.
Therefore, non-array instances successfully validate against this
keyword. If needed, make use of the type keyword to constraint
the accepted type accordingly.
Examples
{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"uniqueItems": true
}[ 1, "hello", true, { "name": "John" } ][ { "name": "John" }, 1, "hello", true, { "name": "John" } ][]"Hello World"{
"$schema": "https://json-schema.org/draft/2020-12/schema",
"uniqueItems": false
}[ 1, "hello", true, { "name": "John" } ][ { "name": "John" }, 1, "hello", true, { "name": "John" } ][]"Hello World"