Useful Jinja Filters and Extension in APIO

Key Filters

• tojson: Converts a dictionary to a JSON Object.

{{ data | tojson }}

• json: Converts a JSON string into a dictionary for further manipulation.

{{ context.response | json }}

• pp_dict: Formats a dictionary into a pretty-printed JSON Object.

{{ data | pp_dict }}

• combine: Merges dictionaries.

{{ request.body | combine(context.response | json) }}

• dict_filter: Filters dictionary entries by key.

{{ request.body | dict_filter("firstName") }}

• default: It ensures a value defaults to something else if it’s undefined or falsy.

{{ data | default(default_value) }}

• If data is falsy or undefined, it uses default_value instead. Examples of default_value: "default value", 42, [1, 2, 3].
• If data is truthy, its value is used directly.

Using Python-like Jinja filters

Jinja templates in APIO allow you to leverage Python-like commands and filters to manipulate data dynamically. This section explains how to use these commands, including an example of decoding Base64-encoded strings.

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Example: Decoding Base64 Strings

Base64 encoding is commonly used to encode data for safe transmission. You can use the built-in b64decode filter in Jinja to decode a Base64-encoded string stored in a context variable.

Basic Decoding To decode a Base64-encoded string:

{{ coded_string | b64decode }}

• Input Example:

  {
      "context": {
          "coded_string": "U29tZSB0ZXh0IHRvIGRlY29kZQ=="
      }
  }

• Template:

  Decoded String: {{ coded_string | b64decode }}

• Output:

  Decoded String: Some text to decode

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Handling Incorrect Padding If the Base64-encoded string is padded incorrectly (e.g., missing the necessary = padding at the end), decoding will fail. You can dynamically add the required padding by calculating how much is missing and appending it before decoding:

{{ (coded_string + (4 - (coded_string | length % 4)) * '=') | b64decode }}

• Explanation:

  • (4 - (coded_string | length % 4)): Determines the number of padding characters (=) needed to make the string’s length a multiple of 4.
  • coded_string + ...: Appends the required padding (=).
  • | b64decode: Decodes the properly padded string.

• Example Input:

  {
      "context": {
          "coded_string": "U29tZSB0ZXh0IHRvIGRlY29kZQ"
      }
  }

• Template:

  Decoded String: {{ (coded_string + (4 - (coded_string | length % 4)) * '=') | b64decode }}

• Output:

  Decoded String: Some text to decode

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Other Python-Like Commands in Jinja

String Transformations

• Convert to uppercase:

  {{ my_string | upper }}

• Convert to lowercase:

  {{ my_string | lower }}

Mathematical Operations

• Perform calculations:

  {{ (value1 + value2) * 3 }}

Data Formatting

• Format numbers:

  {{ value | round(2) }}

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Key Points

• Python-like filters, such as b64decode, make it easy to manipulate data within Jinja templates.
• You can combine basic math operations and string manipulations directly in Jinja to handle edge cases (e.g., incorrect Base64 padding).
• These features provide flexibility and adaptability when working with dynamic workflows.