Circular Dependencies

Handling circular FK dependencies between tables.

Circular Dependencies

Real-world schemas often have circular foreign key dependencies. Seedling handles these with multi-pass generation.

Detection

During planning, Seedling detects cycles in the FK dependency graph:

When a cycle is detected, it is split into pass groups. Tables in a cycle are generated together across multiple passes.

Nullable Circular FKs

If at least one column in the cycle is nullable:

1. Pass 1: Generate rows with NULL in the nullable FK
2. Pass 2: Update the NULL FKs with valid references

This is the simplest and most performant approach.

Non-Nullable Circular FKs

If all columns in a cycle are NOT NULL:

1. Use SET CONSTRAINTS ALL DEFERRED within a transaction
2. Generate all rows without FK validation
3. Commit — deferred constraints are checked at commit time

This requires the database to support deferred constraints (Postgres supports this; MySQL does not).

Many-to-Many Join Tables

Join tables (e.g., users_roles) are handled by:

1. Generating both parent tables first
2. Generating the join table with FK references to both parents
3. Configurable join factor (how many links per parent row)

users_roles:
  user_id:
    generator: fk_pool
    params:
      strategy: weighted
      join_factor: 3
  role_id:
    generator: fk_pool
    params:
      strategy: uniform