# DBML - Full Syntax Docs

DBML (database markup language) is a simple, readable DSL language designed to define database structures. This page outlines the full syntax documentations of DBML.

# Take a look at an example below:
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

# Project Definition

You can give overall description of the project.

Project project_name {
  database_type: 'PostgreSQL'
  Note: 'Description of the project'
}

# 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 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

You can add notes to the table, and refer to them in the visual plane.

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

    Note: 'Stores user data'
}

# 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.

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

    Example, [headercolor: #3498db]

# Column Definition

# Column Settings

Each column can take have optional 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
  • increment: mark the column as auto-increment

# Default Value

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

Indexes allow users to quickly locate and access the data. Users can define single or multi-column indexes.

Table bookings {
  id integer
  country varchar
  booking_date date
  created_at timestamp

  indexes {
      (id, country) [pk] // composite primary key
      created_at [note: '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
  • pk: primary key

# 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]
}

# Relationship settings

Ref: products.merchant_id > merchants.id [delete: cascade, update: no action]
  • delete / update: cascade | restrict | set null | set default | no action
    Define referential actions. Similar to ON DELETE/UPDATE CASCADE/... in SQL.

Relationship settings are not supported for inline form ref.

# 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

# Note Definition

Note allows users to give description for a particular DBML element.

Table users {
  id int [pk]
  name varchar

  Note: 'This is a note of this table'
  // or
  Note {
    'This is a note of this table'
  }
}

Note's value is a string. If your note spans over multiple lines, you can use multi-line string to define your note.

# Project Notes

Project DBML {
  Note: '''
    # 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](http://dbdiagram.io)
  '''
}

# Table Notes

Table users {
  id int [pk]
  name varchar

  Note: 'Stores user data'
}

# 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
    ']
} 

# Multi-line String

Multiline string will be defined between triple single quote '''

Note: '''
  This is a block string
  This string can spans over multiple lines.
'''
  • Line breaks: <enter> key

  • Line continuation: \ backslash

  • Escaping characters:

    • \: using double backslash \\
    • ''': using \'''
  • The number of spaces you use to indent a block string will be the minimum number of leading spaces among all lines. The parser will automatically remove the number of indentation spaces in the final output. The result of the above example will be:

    This is a block string
    This string can spans over multiple lines.
    

# 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

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
  • triple quote as '''multi-line string''': multi-line string value
  • backtick `: function expression