ptzagk / dbml

Database Markup Language (DBML), designed to define database structures

DBML - Database Markup Language

DBML (database markup language) is a simple, readable DSL language designed to define database structures.

Benefits

• It is simple, flexible and highly human-readable
• It is database agnostic, focusing on the essential database structure definition without worrying about the detailed syntaxes of each database
• Comes with a free, simple database visualiser at dbdiagram.io

Command-Line Interface (CLI)

(coming soon) A dbml-to-sql generator to generate SQL from .dbml file

• Allow users to integrate DBML with their workflow
• Each project will have one or several .dbml files to define database schema
• DBML-CLI will be used to export .dbml files to specific SQL (MySQL, PostgreSQL, etc), JSON format, etc
• DBML-CLI could also be used to generate .dbml files from other SQL or JSON files

Example

Example of a database definition of a simple blogging site:

Table users {
    id integer
    username varchar
    role varchar
    created_at timestamp
}

Table posts {
    id integer [primary key]
    title varchar
    body text [note: 'Content of the post']
    user_id integer
    created_at timestamp
}

Ref: posts.user_id > users.id // many-to-one

Is this similar to SQL DDL?

Not quite. Despite its name (data "definition" language), DDL is designed mainly to help physically create, modify or remove tables, not to define them.

DDL also comes with a few more drawbacks:

• It is hard to read, especially when trying to add multiple column/table settings together.
• It is database specific (Oracle vs PostgreSQL vs MySQL, etc)
• Since it is imperative (vs declarative), to fully reconstruct a table definition you have to trace through all the code (instead of focusing on just 1 single section).

How to generate SQL from DBML?

1. Go to dbdiagram.io
2. Type up your DBML code
3. Go to Export > SQL (choose your DB)

DBML Full Syntax Docs

DBML supports defining the following:

• Table Definition
  • Table Alias
  • Table Notes (coming soon)
  • Table Settings
• Column Definition
  • Column Settings
  • Default Value (NEW)
  • Index Definition (NEW)
    • Index Settings
• Relationships & Foreign Key Definitions
  • Many-to-many relationship
• Comments
• Metadata Column Notes
• Enum Definition
• TableGroup (coming soon)
• Syntax Consistency
• Community Contributions
  • Emacs Mode for DBML

Table Definition

Table table_name {
    column_name column_type [column_settings]
}

• title of database table is listed as table_name
• name of the column is listed as column_name
• type of the data in the column listed as column_type
  • supports all data types, as long as it is a single word (remove all spaces in the data type). Example, JSON, JSONB, decimal(1,2), etc.
• list is wrapped in curly brackets {}, for indexes, constraints and table definitions
• settings are wrapped in square brackets []
• string value is to be wrapped in a single quote as 'string'
• column_name can be stated in just plain text, or wrapped in a double quote as "column name"

Table Alias: You can alias the table, and use them in the references later on.

Table very_long_user_table as U {
    ...
}

Ref: U.id < posts.user_id

Table Notes (coming soon): You can add notes to the table, and refer to them in the visual plane.

Table users {
    id integer
    status varchar [note: 'status']

    [note: 'Contains all users information']
}

Table Settings: Settings are all defined within square brackets: [setting1: value1, setting2: value2, setting3, setting4]

Each setting item can take in 2 forms: Key: Value or keyword, similar to that of Python function parameters.

• color: <color_code>: change the table header color (coming soon)

  Example, [color: #3498db]

Column Definition

Column Settings: Each column can take have optinal settings, defined in square brackets like:

Table buildings {
    ...
    address varchar(255) [unique, not null, note: 'to include unit number']
    id integer [ pk, unique, default: 123, note: 'Number' ]
}

The list of column settings you can use:

• note: 'string to add notes': add a metadata note to this column
• primary key or pk: mark a column as primary key. For composite primary key, refer to the 'Indexes' section
• null or not null: mark a column null or not null
• unique: mark the column unique
• default: some_value: set a default value of the column, please refer to the 'Default Value' section below (NEW)
• increment: mark the column as auto-increment (NEW)

Default Value (NEW): You can set default value as:

• number value starts blank: default: 123 or default: 123.456
• string value starts with single quotes: default: 'some string value'
• expression value is wrapped with parenthesis: default: `now() - interval '5 days'`
• boolean (true/false/null): default: false or default: null

Example,

Table users {
    id integer [primary key]
    username varchar(255) [not null, unique]
    full_name varchar(255) [not null]
    gender varchar(1) [default: 'm']
    created_at timestamp [default: `now()`]
    rating integer [default: 10]
}

Index Definition (NEW): Indexes allow users to quickly locate and access the data. Users can define single or multi-column indexes.

Table bookings {
  id integer [primary key]
  country varchar
  booking_date date
  created_at timestamp

  indexes {
      created_at [name: 'Date']
      booking_date
      (country, booking_date) [unique]
      booking_date [type: hash]
      (`id*2`)
      (`id*3`,`getdate()`)
      (`id*3`,id)
  }
}

There are 3 types of index definitions:

• Index with single field (with index name): CREATE INDEX on users (created_at)
• Index with multiple fields (composite index): CREATE INDEX on users (created_at, country)
• Index with an expression: CREATE INDEX ON films ( first_name + last_name )
• (bonus) Composite index with expression: CREATE INDEX ON users ( country, (lower(name)) )

Index Settings

• type: type of index (btree, gin, gist, hash depending on DB). For now, only type btree and hash are accepted.
• name: name of index
• unique: unique index

Relationships & Foreign Key Definitions

Relationships are used to define foreign key constraints between tables.

Table posts {
    id integer [primary key]
    user_id integer [ref: > users.id] // many-to-one
}

// or this
Table users {
    id integer [ref: < posts.user_id, ref: < reviews.user_id] // one to many
}

// The space after '<' is optional

There are 3 types of relationships: one-to-one, one-to-many, and many-to-one

• <: one-to-many. E.g: users.id < posts.user_id
• >: many-to-one. E.g: posts.user_id > users.id
• -: one-to-one. E.g: users.id - user_infos.user_id

In DBML, there are 3 syntaxes to define relationships:

//Long form
Ref name_optional {
  table1.column1 < table2.column2
}

//Short form:
Ref name_optional: table1.column1 < table2.column2

// Inline form
Table posts {
    id integer
    user_id integer [ref: > users.id]
}

Many-to-many relationship

For many-to-many relationship, we don't have a syntax for it as we believe it should be represented as 2 many-to-one relationships. For more information, please refer to https://www.holistics.io/blog/dbdiagram-io-many-to-many-relationship-diagram-generator-script/

Comments

You can comment in your code using //, so it is easier for you to review the code later.

Example,

// order_items refer to items from that order

Metadata Column Notes

You can add notes to your columns, so you can easily refer to it when hovering over the column in the diagram canvas.

column_name column_type [note: 'replace text here']

Example,

Table orders {
    status varchar [
    note: '
    💸 1 = processing, 
    ✔️ 2 = shipped, 
    ❌ 3 = cancelled,
    😔 4 = refunded
    ']
}

Enum Definition

Enum allows users to define different values of a particular column. When hovering over the column in the canvas, the enum values will be displayed.

enum job_status {
    created [note: 'Waiting to be processed']
    running
    done
    failure
}

Table jobs {
    id integer
    status job_status
}

TableGroup (coming soon)

TableGroup allows users to group the related or associated tables together.

TableGroup tablegroup_name { // tablegroup is case-insensitive.
    table1 
    table2 
    table3
}

//example
TableGroup e-commerce1 {
    merchants
    countries
}

Syntax Consistency

DBML is the standard language for database and the syntax is consistent to provide clear and extensive functions.

• curly brackets {}: grouping for indexes, constraints and table definitions
• square brackets []: settings
• forward slashes //: comments
• column_name is stated in just plain text
• single quote as 'string': string value
• double quote as "column name": quoting variable
• backtick `: function expression

Community Contributions

Emacs Mode for DBML

(Contributed by ccod): https://github.com/ccod/dbd-mode