Value Generators

If you want Lightblue to automatically populate fields (e.g. generate id or current date), then you need to define a value generator. Behavior:

• if a field is not in the document and is not required, it won't be automatically populated,
• if a field is required and it is not in the document, it'll be inserted and automatically populated,
• if a field is set to null, it will be automatically populated (even if not required),
• if overwrite configuration flag is set to true on the value generator, field will be populated with a generated value even if it is initialized (already has a value) and even if it's set in the request. It will not be inserted if the field is not required and if the field does not exist in the document.

Note: Value Generators are available since Lightblue version 1.7.0.

Generator types available:

UUID

Generates a value from java.util.UUID.randomUUID(). Replaces uid type.

            "_id": {
                "type": "string",
                "constraints": {
                    "identity": true
                },
                "valueGenerator": {
                    "type": "UUID"
                }
            },

IntSequence

As it's name implies, the IntSequence value generator generates integer numbers in a sequence. It's primary use case is generating numeric identifiers for documents (approach which is often used in RDBMS).

Here is how _ids were defined so far:

            "_id": {
                "type": "uid",
                "constraints": {
                    "identity": true
                }
            },

Uid type is about to be deprecated. UUID generator is to be used instead. Since this section is about IntSequence generator only, I will stop here.

Here is how you can define IntSequence _id:

            "_id": {
                "type": "integer",
                "constraints": {
                    "identity": true
                },
                "valueGenerator": {
                    "type": "IntSequence",
                    "configuration": {
                        "initialValue": "10000",
                        "name": "termsIdIntSequence"
                    }
                },

Important:

• IntSequence generator name needs to be unique and self-explainatory. Recommended naming pattern: <entityName><fieldName><valueGeneratorType>.
• Generator is defined at the field level, in the versioned schema. This means that multiple versions can exist defining different generators (or complete lack of thereof) for the same field.
• In the example above, type of the field was changed from "uid" to "integer". This is a breaking change and may require data conversion. Note that you could change the type from "uid" to "string" instead (not a breaking change and IntSequence generator would still work as expected), but you'd loose type safety this way (not recommended).

CurrentTime

Uses new java.util.Date() to poulate the field.

Create:

            "creationDate": {
                "type": "date",
                "constraints": {
                    "required": true
                },
                "valueGenerator": {
                    "type": "CurrentTime"
                }
            }

Update:

            "updateTime": {
                "type": "date",
                "valueGenerator": {
                    "type": "CurrentTime",
                    "overwrite": true
                }
            }

Note the overwrite flag.