Schema Design Skill

Reference guide for Butterbase's declarative schema DSL. Covers column types, constraints, indexes, and common data modeling patterns.

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1. Overview

Butterbase uses a declarative schema DSL — you describe the desired end state of your database, and the platform computes and applies the diff. You never write raw ALTER TABLE or CREATE TABLE SQL. Instead, call manage_schema with action: "apply" and a JSON payload describing your tables, columns, and indexes.

The single manage_schema tool exposes four actions:

Action	Purpose
"get"	Read the current schema
"dry_run"	Preview SQL that apply would execute, without running it
"apply"	Apply a declarative schema (diffs against current, runs safe DDL)
"list_migrations"	List applied migrations, most recent first

Key principles:

• Idempotent: applying the same schema twice is safe — returns "Schema is up to date" if no changes needed
• Additive by default: new columns and tables are created automatically
• Explicit drops: destructive operations require opt-in via _drop / _dropColumns
• Preview first: use action: "dry_run" to see what will change before committing
• Transactional: each migration runs in a single transaction — all changes commit or all roll back

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2. Column Types Reference

Type	PostgreSQL	Use case
uuid	UUID	Primary keys, foreign keys
text	TEXT	Strings of any length
integer	INTEGER	Whole numbers (-2B to 2B)
bigint	BIGINT	Large whole numbers
boolean	BOOLEAN	True/false flags
timestamptz	TIMESTAMPTZ	Dates with timezone
jsonb	JSONB	Structured/semi-structured data
real	REAL	32-bit floating point
double precision	DOUBLE PRECISION	64-bit floating point
vector(N)	VECTOR(N)	Embeddings (pgvector); e.g. vector(1536) for OpenAI

Always use timestamptz instead of timestamp. timestamp silently drops timezone info and causes subtle bugs with users in different time zones.

---

3. Column Properties

Each column is an object with the following properties:

Property	Type	Required	Default	Description
type	string	✅ yes	—	Column data type (see §2)
primaryKey	boolean	no	false	Mark as primary key
nullable	boolean	no	true	Allow NULL values
default	string	no	—	SQL expression for default value
unique	boolean	no	false	Add unique constraint
references	string | object	no	—	Foreign key target (see below)

Foreign keys — short or long form

Short form (just the target):

"author_id": { "type": "uuid", "nullable": false, "references": "users.id" }

Long form (with cascade behavior):

"author_id": {
  "type": "uuid",
  "nullable": false,
  "references": {
    "table": "users",
    "column": "id",
    "onDelete": "CASCADE",
    "onUpdate": "NO ACTION"
  }
}

onDelete / onUpdate accept CASCADE | SET NULL | SET DEFAULT | RESTRICT | NO ACTION (default NO ACTION).

Default expressions

Pass SQL expressions as strings:

"default": "gen_random_uuid()"   // UUID primary keys
"default": "now()"               // Timestamps
"default": "false"               // Booleans
"default": "0"                   // Integers
"default": "'draft'"             // String literals (single-quoted)

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4. Standard Base Pattern

Every table should include these base columns:

{
  "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
  "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
  "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
}

If your app uses Row-Level Security (RLS), also add:

"user_id": { "type": "uuid", "nullable": false, "references": "users.id" }

Tables without user_id cannot have per-user RLS policies applied later without a migration.

---

5. Index Types

method	Use case	Example opclass
btree	Default, range queries, sorting	—
hash	Exact-match lookups	—
gin	Full-text search on JSONB, arrays	jsonb_path_ops
gist	Geometric/spatial data	—
hnsw	Vector similarity (pgvector)	vector_cosine_ops
ivfflat	Vector similarity (large datasets)	vector_cosine_ops

Index definition format

Indexes are defined per-table under the indexes key:

{
  "indexes": {
    "idx_posts_author": {
      "columns": ["author_id"],
      "method": "btree"
    },
    "idx_posts_embedding": {
      "columns": ["embedding"],
      "method": "hnsw",
      "opclass": "vector_cosine_ops"
    },
    "idx_posts_content_search": {
      "columns": ["content"],
      "method": "gin"
    }
  }
}

Index naming convention: idx_{table}_{column(s)} — e.g. idx_orders_user_id.

Composite indexes

"idx_members_workspace_user": {
  "columns": ["workspace_id", "user_id"],
  "method": "btree",
  "unique": true
}

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6. Using manage_schema

All schema operations go through one tool with an action parameter:

manage_schema({ app_id, action: "get" })
manage_schema({ app_id, action: "dry_run", schema })
manage_schema({ app_id, action: "apply", schema, name })   // name is optional
manage_schema({ app_id, action: "list_migrations" })

Creating new tables

Include the table definition in your schema payload and call action: "apply". The platform creates the table if it doesn't exist.

Adding columns to existing tables

Add the new column(s) to the existing table definition and call action: "apply". Existing rows receive the column's default value (or NULL if no default).

Destructive operations

Dropping tables and columns is opt-in and explicit. Without _drop / _dropColumns, the platform refuses with STATE_PREREQUISITE_MISSING.

{
  "schema": {
    "_drop": ["old_table_name", "another_old_table"]
  }
}

Dropping columns from a specific table:

{
  "schema": {
    "posts": {
      "_dropColumns": ["legacy_field", "unused_col"],
      "columns": { ... }
    }
  }
}

⚠️ Drops are irreversible. Always run action: "dry_run" first.

Preview before commit

Use the same payload with action: "dry_run" to see the SQL that apply would execute — without touching the database:

// Preview only:
manage_schema({ app_id, action: "dry_run", schema })

// Commit:
manage_schema({ app_id, action: "apply", schema, name: "add_posts_table" })

Common errors

Code	Meaning
VALIDATION_INVALID_SCHEMA	Schema format doesn't match the DSL
STATE_PREREQUISITE_MISSING	Destructive op without _drop / _dropColumns
QUOTA_TABLE_LIMIT	Exceeds the per-app table limit
RESOURCE_NOT_FOUND	app_id does not exist

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7. Complete Patterns

A) Blog / CMS

{
  "app_id": "YOUR_APP_ID",
  "action": "apply",
  "schema": {
    "users": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "email": { "type": "text", "nullable": false, "unique": true },
        "name": { "type": "text", "nullable": false },
        "avatar_url": { "type": "text" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_users_email": { "columns": ["email"], "method": "btree", "unique": true }
      }
    },
    "categories": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "name": { "type": "text", "nullable": false, "unique": true },
        "slug": { "type": "text", "nullable": false, "unique": true },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      }
    },
    "posts": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "author_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "category_id": { "type": "uuid", "references": "categories.id" },
        "title": { "type": "text", "nullable": false },
        "slug": { "type": "text", "nullable": false, "unique": true },
        "content": { "type": "text" },
        "excerpt": { "type": "text" },
        "published": { "type": "boolean", "nullable": false, "default": "false" },
        "published_at": { "type": "timestamptz" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_posts_author_id": { "columns": ["author_id"], "method": "btree" },
        "idx_posts_category_id": { "columns": ["category_id"], "method": "btree" },
        "idx_posts_slug": { "columns": ["slug"], "method": "btree", "unique": true },
        "idx_posts_published": { "columns": ["published", "published_at"], "method": "btree" }
      }
    },
    "comments": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "post_id": { "type": "uuid", "nullable": false, "references": "posts.id" },
        "author_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "content": { "type": "text", "nullable": false },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_comments_post_id": { "columns": ["post_id"], "method": "btree" },
        "idx_comments_author_id": { "columns": ["author_id"], "method": "btree" }
      }
    }
  }
}

---

B) E-commerce

{
  "app_id": "YOUR_APP_ID",
  "action": "apply",
  "schema": {
    "products": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "name": { "type": "text", "nullable": false },
        "description": { "type": "text" },
        "price": { "type": "integer", "nullable": false },
        "stock": { "type": "integer", "nullable": false, "default": "0" },
        "sku": { "type": "text", "unique": true },
        "metadata": { "type": "jsonb" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_products_sku": { "columns": ["sku"], "method": "btree", "unique": true },
        "idx_products_metadata": { "columns": ["metadata"], "method": "gin", "opclass": "jsonb_path_ops" }
      }
    },
    "orders": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "user_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "status": { "type": "text", "nullable": false, "default": "'pending'" },
        "total": { "type": "integer", "nullable": false, "default": "0" },
        "shipping_address": { "type": "jsonb" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_orders_user_id": { "columns": ["user_id"], "method": "btree" },
        "idx_orders_status": { "columns": ["status"], "method": "btree" }
      }
    },
    "order_items": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "order_id": { "type": "uuid", "nullable": false, "references": "orders.id" },
        "product_id": { "type": "uuid", "nullable": false, "references": "products.id" },
        "quantity": { "type": "integer", "nullable": false },
        "price": { "type": "integer", "nullable": false },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_order_items_order_id": { "columns": ["order_id"], "method": "btree" },
        "idx_order_items_product_id": { "columns": ["product_id"], "method": "btree" }
      }
    },
    "reviews": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "product_id": { "type": "uuid", "nullable": false, "references": "products.id" },
        "user_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "rating": { "type": "integer", "nullable": false },
        "title": { "type": "text" },
        "body": { "type": "text" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_reviews_product_id": { "columns": ["product_id"], "method": "btree" },
        "idx_reviews_user_id": { "columns": ["user_id"], "method": "btree" }
      }
    }
  }
}

---

C) SaaS Multi-tenant

{
  "app_id": "YOUR_APP_ID",
  "action": "apply",
  "schema": {
    "workspaces": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "name": { "type": "text", "nullable": false },
        "slug": { "type": "text", "nullable": false, "unique": true },
        "plan": { "type": "text", "nullable": false, "default": "'free'" },
        "settings": { "type": "jsonb" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_workspaces_slug": { "columns": ["slug"], "method": "btree", "unique": true }
      }
    },
    "members": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "workspace_id": { "type": "uuid", "nullable": false, "references": "workspaces.id" },
        "user_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "role": { "type": "text", "nullable": false, "default": "'member'" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_members_workspace_user": { "columns": ["workspace_id", "user_id"], "method": "btree", "unique": true },
        "idx_members_user_id": { "columns": ["user_id"], "method": "btree" }
      }
    },
    "projects": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "workspace_id": { "type": "uuid", "nullable": false, "references": "workspaces.id" },
        "name": { "type": "text", "nullable": false },
        "description": { "type": "text" },
        "archived": { "type": "boolean", "nullable": false, "default": "false" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_projects_workspace_id": { "columns": ["workspace_id"], "method": "btree" }
      }
    },
    "tasks": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "project_id": { "type": "uuid", "nullable": false, "references": "projects.id" },
        "assignee_id": { "type": "uuid", "references": "users.id" },
        "title": { "type": "text", "nullable": false },
        "description": { "type": "text" },
        "status": { "type": "text", "nullable": false, "default": "'todo'" },
        "priority": { "type": "text", "nullable": false, "default": "'medium'" },
        "due_date": { "type": "timestamptz" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_tasks_project_id": { "columns": ["project_id"], "method": "btree" },
        "idx_tasks_assignee_id": { "columns": ["assignee_id"], "method": "btree" },
        "idx_tasks_status": { "columns": ["status"], "method": "btree" }
      }
    }
  }
}

---

D) Social App

{
  "app_id": "YOUR_APP_ID",
  "action": "apply",
  "schema": {
    "profiles": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "user_id": { "type": "uuid", "nullable": false, "unique": true, "references": "users.id" },
        "username": { "type": "text", "nullable": false, "unique": true },
        "bio": { "type": "text" },
        "avatar_id": { "type": "uuid" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_profiles_username": { "columns": ["username"], "method": "btree", "unique": true },
        "idx_profiles_user_id": { "columns": ["user_id"], "method": "btree", "unique": true }
      }
    },
    "posts": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "author_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "content": { "type": "text", "nullable": false },
        "media": { "type": "jsonb" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" },
        "updated_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_posts_author_id": { "columns": ["author_id"], "method": "btree" },
        "idx_posts_created_at": { "columns": ["created_at"], "method": "btree" }
      }
    },
    "follows": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "follower_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "following_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_follows_follower_following": { "columns": ["follower_id", "following_id"], "method": "btree", "unique": true },
        "idx_follows_following_id": { "columns": ["following_id"], "method": "btree" }
      }
    },
    "likes": {
      "columns": {
        "id": { "type": "uuid", "primaryKey": true, "default": "gen_random_uuid()" },
        "user_id": { "type": "uuid", "nullable": false, "references": "users.id" },
        "post_id": { "type": "uuid", "nullable": false, "references": "posts.id" },
        "created_at": { "type": "timestamptz", "nullable": false, "default": "now()" }
      },
      "indexes": {
        "idx_likes_user_post": { "columns": ["user_id", "post_id"], "method": "btree", "unique": true },
        "idx_likes_post_id": { "columns": ["post_id"], "method": "btree" }
      }
    }
  }
}

---

8. Anti-Patterns

• Using timestamp instead of timestamptz — timestamp silently drops timezone info, causing subtle bugs for users in different time zones. Always use timestamptz.

• Forgetting "default": "gen_random_uuid()" on UUID primary keys — Without a default, inserts will fail unless the caller explicitly provides an ID. Always set this default.

• Omitting created_at / updated_at columns — These are essential for debugging, ordering, and audit trails. Include them on every table from the start; retrofitting them is painful.

• Not adding a user_id column on tables that will need RLS — Row-Level Security policies require a user_id column to exist. Adding it later requires a migration and backfill. Plan ahead.

• Over-indexing — Indexes speed up reads but add overhead to every write. Only index columns you actively query or sort by. Avoid indexing every column "just in case."

• Using text for booleans or enums — Use the boolean type for true/false values. For enums, text is acceptable but consider adding a CHECK constraint or a lookup table for referential integrity.

• Storing file URLs directly — URLs change (CDN migrations, domain changes). Store the object's UUID (avatar_id uuid) and resolve the URL at render time using generate_download_url. This decouples your data from your storage topology.

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If a docs/butterbase/00-state.md exists in the working directory, prefer invoking via /butterbase-skills:journey-schema so the journey orchestrator stays in sync.