Dct Generate

• schema: JSON schema as a file path or inline JSON string

Flags

• -n, --lines <number>: Number of rows to generate (default: 1)
• -f, --format <format>: Output format - csv, ndjson (default: csv)
• -o, --outfile <file>: Output file path (default: stdout)

Examples

From schema file:

dct gen schema.json -n 1000 -o test_data.csv

Inline schema:

dct gen '[{"field":"name","source":"firstNames"}]' -n 100

NDJSON output:

dct gen schema.json -n 500 -f ndjson -o output.ndjson

Generate to stdout:

dct gen users-schema.json -n 10

Schema Format

Array of field objects:

[
  {
    "field": "column_name",
    "source": "source_type",
    "config": { ... }
  }
]

Available Data Sources

Random Generators

• randomBool - Boolean true/false

  {"field": "active", "source": "randomBool"}
  

• randomEnum - Random value from list

  {"field": "status", "source": "randomEnum", "config": {"values": ["pending", "active", "inactive"]}}
  

• randomAscii - Random ASCII string

  {"field": "code", "source": "randomAscii", "config": {"length": 10}}
  

• randomUniformInt - Uniform integer distribution

  {"field": "age", "source": "randomUniformInt", "config": {"min": 18, "max": 65}}
  

• randomNormal - Normal/Gaussian distribution

  {"field": "score", "source": "randomNormal", "config": {"mean": 100, "std": 15}}
  

• randomPoisson - Poisson distribution

  {"field": "events", "source": "randomPoisson", "config": {"lambda": 5}}
  

• randomDatetime - Random date/time

  {"field": "created_at", "source": "randomDatetime", "config": {"min": "2024-01-01 00:00:00", "max": "2024-12-31 23:59:59", "tz": "UTC"}}
  

• randomDate - Random date

  {"field": "birth_date", "source": "randomDate", "config": {"min": "1980-01-01", "max": "2005-12-31"}}
  

• randomTime - Random time

  {"field": "meeting_time", "source": "randomTime", "config": {"min": "09:00:00", "max": "17:00:00"}}
  

Data Generators

• uuid - UUID v4

  {"field": "id", "source": "uuid"}
  

• firstNames - Random first names

  {"field": "first_name", "source": "firstNames"}
  

• lastNames - Random last names

  {"field": "last_name", "source": "lastNames"}
  

• companies - Company names

  {"field": "company", "source": "companies"}
  

• emails - Email addresses

  {"field": "email", "source": "emails"}
  

Derived Fields

Create computed fields using the Expr language:

{
  "field": "full_name",
  "source": "derived",
  "config": {
    "fields": ["first_name", "last_name"],
    "expression": "first_name + ' ' + last_name"
  }
}

Complex expressions:

{
  "field": "display_name",
  "source": "derived",
  "config": {
    "fields": ["first_name", "last_name", "company"],
    "expression": "first_name + ' ' + last_name + ' (' + company + ')'"
  }
}

Complete Schema Example

[
  {"field": "id", "source": "uuid"},
  {"field": "first_name", "source": "firstNames"},
  {"field": "last_name", "source": "lastNames"},
  {"field": "email", "source": "emails"},
  {"field": "age", "source": "randomUniformInt", "config": {"min": 18, "max": 65}},
  {"field": "department", "source": "randomEnum", "config": {"values": ["Engineering", "Sales", "Marketing", "HR"]}},
  {"field": "salary", "source": "randomNormal", "config": {"mean": 75000, "std": 15000}},
  {"field": "is_active", "source": "randomBool"},
  {
    "field": "full_name",
    "source": "derived",
    "config": {
      "fields": ["first_name", "last_name"],
      "expression": "first_name + ' ' + last_name"
    }
  }
]

Best Practices

• Generate small samples first (n=10) to verify schema
• Use derived fields to create realistic relationships
• Use NDJSON format for nested/complex data
• Save schemas to files for reuse
• Use appropriate distributions for realistic data

Output Formats

CSV (default):

id,first_name,age
550e8400-e29b-41d4-a716-446655440000,John,34

NDJSON:

{"id":"550e8400-e29b-41d4-a716-446655440000","first_name":"John","age":34}
{"id":"550e8400-e29b-41d4-a716-446655440001","first_name":"Jane","age":28}

Related Skills

• dct-peek: Verify generated data looks correct
• dct-infer: Check schema of generated data
• dct-diff: Compare generated data with production samples