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ajv-merge-patch
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$merge and $patch keywords for Ajv JSON-Schema validator to extend schemas
$merge and $patch keywords for Ajv JSON-Schema validator to extend JSON-schemas
The keywords $merge
and $patch
allow to extend the JSON-schemas using patches in the format JSON Merge Patch (RFC 7396) or JSON Patch (RFC 6902).
Schema extension is necessary if you want to add additional properties to the recursive schema (e.g. meta-schema). Consider this example:
Original schema:
{
"id": "mySchema.json#",
"type": "object",
"properties": {
"foo": { "type": "string" },
"bar": { "$ref": "#" }
},
"additionalProperties": false
}
Valid data: { foo: 'a' }
, { foo: 'a', bar: { foo: 'b' } }
etc.
If you want to define schema that would allow more properties, the only way to do it without $merge
or $patch
keywords is to copy-paste and edit the original schema.
Using $merge
keyword you can create an extended schema in this way:
{
"id": "mySchemaExtended.json#",
"$merge": {
"source": { "$ref": "mySchema.json#" },
"with": {
"properties": {
"baz": { "type": "number" }
}
}
}
}
Valid data: { foo: 'a', baz: 1 }
, { foo: 'a', baz: 1, bar: { foo: 'b', baz: 2 } }
, etc.
$merge
is implemented as a custom macro keyword using json-merge-patch package.
The same schema extension using $patch
keyword:
{
"id": "mySchemaExtended.json#",
"$patch": {
"source": { "$ref": "mySchema.json#" },
"with": [
{
"op": "add",
"path": "/properties/baz",
"value": { "type": "number" }
}
]
}
}
$patch
is implemented as a custom macro keyword using fast-json-patch package.
In the majority of cases $merge
format is easier to understand and to maintain. $patch
can be used for extensions and changes that cannot be expressed using $merge
.
with
property in keywords can also be a reference to a part of some schema, in which case the resolved value will be used rather than the actual object with property $ref
.
Please note:
source
schema or the patch in with
keyword use $ref
, they won't take into account the resolution scope for their internal $refs defined by the parent objects - they will be used as separate objects.$ref
in both source
schema and with
patch take into account current $ref resolution scope (from version 2.0.0).See also:
These keywords are compatible with Ajv version >=5.1.0-beta.0.
To add these keywords to Ajv instance:
var Ajv = require('ajv');
var ajv = new Ajv();
require('ajv-merge-patch')(ajv);
You can include these keywords in your code using browserify.
To include only $merge
keyword:
require('ajv-merge-patch/keywords/merge')(ajv);
To include only $patch
keyword:
require('ajv-merge-patch/keywords/patch')(ajv);
FAQs
$merge and $patch keywords for Ajv JSON-Schema validator to extend schemas
The npm package ajv-merge-patch receives a total of 28,229 weekly downloads. As such, ajv-merge-patch popularity was classified as popular.
We found that ajv-merge-patch demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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