Basic Concepts

Configuration Structure

A datafake configuration is a JSON object with three optional sections:

{
    "metadata": { ... },
    "variables": { ... },
    "schema": { ... }
}

Metadata

Optional information about the configuration:

{
    "metadata": {
        "name": "User Generator",
        "version": "1.0.0",
        "description": "Generates fake user data"
    }
}

Variables

Pre-generate values that can be reused across the schema:

{
    "variables": {
        "userId": {"fake": ["uuid"]},
        "createdAt": {"fake": ["datetime"]}
    },
    "schema": {
        "id": {"var": "userId"},
        "audit": {
            "createdBy": {"var": "userId"},
            "createdAt": {"var": "createdAt"}
        }
    }
}

Schema

The schema defines the structure of the generated output. It uses JSONLogic operators, with the fake operator being the most important.

The fake Operator

The fake operator generates fake data of a specified type:

{"fake": ["type"]}
{"fake": ["type", arg1, arg2]}

Simple Types

{"fake": ["uuid"]}
{"fake": ["name"]}
{"fake": ["email"]}

Types with Arguments

Some types accept arguments for customization:

{"fake": ["u8", 18, 65]}     // Integer between 18 and 65
{"fake": ["password", 8, 16]} // Password with 8-16 characters
{"fake": ["words", 5]}        // 5 random words

JSONLogic Operators

datafake-rs supports all standard JSONLogic operators. Here are some commonly used ones:

Variable Access

Reference variables with var:

{"var": "userId"}
{"var": "user.name"}

String Concatenation

Combine strings with cat:

Conditional Logic

Use if for conditional generation:

Arrays

Generate arrays with map:

{
    "schema": {
        "tags": {"map": [
            [1, 2, 3],
            {"fake": ["word"]}
        ]}
    }
}

Nested Objects

Create complex nested structures:

Error Handling

Invalid configurations will result in clear error messages:

• ConfigParse - Invalid JSON syntax
• InvalidConfig - Missing required fields
• FakeOperatorError - Unknown fake type or invalid arguments
• VariableNotFound - Referenced variable doesn’t exist