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YAML 101

YAML is the preferred choice for writing Profile Builder files due to its simplicity and ease of use.

This guide explains the base concepts, syntax, and best practices for writing code in YAML.

What is YAML?

YAML, short for YAML Ain’t Markup Language or Yet Another Markup Language, is a data serialization format often used in config files and exchange of data. A YAML file uses indentation, specific characters, and line breaks for representing various data structures.

Sample YAML file

Below is how a sample YAML document looks like. It contains key-value pairs where the keys are on the left, followed by a colon (:), and the associated values are on the right. The hierarchy and data structure is defined using indentation. The next section explains this in more detail.

# This is a comment
person:
  name: Ruddy Buddy # Note the spacing used for indentation
  age: 42
  is_employed: true
  address: # An object called address
    street: Jefferson Davis Highway
    city: Ruther Glen
    state: Vermont
    phone: 555-90-210
  favorite_sports: # A list
    - soccer
    - baseball

The above code has details of an object called person with properties like name, age, gender, is_student, address and favorite sports.

Here’s how the same YAML file looks in the JSON format:

{
  "person": {
    "name": "Ruddy Buddy",
    "age": 42,
    "is_employed": true,
    "address": {
      "street": "Jefferson Davis Highway",
      "city": "Ruther Glen",
      "state": "Vermont",
      "phone": "555-90-210"
    },
    "favorite_sports": [
      "soccer",
      "baseball"
    ]
  }
}

Indentation

In YAML, the indentation is done using spaces - to define the structure of data. Throughout the YAML file, the number of spacing should be consistent. Typically, we use two spaces for indentation. YAML is whitespace-sensitive, so do not mix spaces and tabs.

# Example of correct indentation
person:
  name: Ruddy Buddy # We used 2 spaces
  age: 42

# Example of incorrect indentation
person:
  name: Ruddy Buddy 
    age: 42 # We mixed spacing and tabs

Comments

As shown above, YAML has single-line comments that start with hash (#) symbol, for providing additional explanation or context in the code. Comments are used to improve readability and they do not affect the code’s functionality.

# YAML comment
person:
  name: Ruddy Buddy # Name of the person
  age: 42 # Age of the person

Data types in YAML

YAML supports several data types:

• Scalars: Represent strings, numbers, and boolean values.
• Sequences: Represent lists and are denoted using a hyphen (-).
• Mappings: Key-value pairs used to define objects or dictionaries using colon (:).

# Example of data types in YAML
person:
  name: Ruddy Buddy # Scalar (string)
  age: 42 # Scalar (number)
  is_employed: true # Scalar (boolean)
  address: # Mapping (object)
    street: Jefferson Davis Highway
    city: Ruther Glen
    state: Vermont
    phone: 555-90-210
  favorite_sports: # Sequence (list)
    - soccer
    - baseball

Chomp modifiers

YAML provides two chomp modifiers for handling line breaks in scalar values.

• >: Removes all newlines and replaces them with spaces.

description: >
  Here is an example of long description
  which has multiple lines. Later, it
  will be converted into a single line.  

• |: Preserves line breaks and spaces.

description: |
  Here is another long description, however
  it will preserve newlines and so the original
  format shall be as-it-is.  

Special characters

You can use escape symbols for special characters in YAML. For example, writing an apostrophe in description can cause the YAML parser to fail. In this case, you can use the escape character.

Best practices for writing YAML

Follow these best practices for writing clean YAML code in your Profiles projects:

• Always keep consistent indentation (preferably spaces over tabs).
• Give meaningful names to your keys.
• Avoid excessive nesting.
• YAML is case sensitive, so be mindful of that.
• Add comments wherever required.
• Use blank lines to separate sections like ID stitcher, feature table, etc.
• If your strings contain special characters, then use escape symbols.
• Make sure you end the quotes in strings to avoid errors.
• Use chomp modifiers for multi-line SQL.

Conclusion

The above guidelines constitute some best practices to write effective Builder code in Profiles. You can also see the following references:

• YAML for VS Code: Extension for comprehensive YAML support in Visual Studio Code.
• YAML Lint for linting.

For more information or in any case of any issues, contact the RudderStack team.

Questions? Contact us by email or on Slack