string_extensions

CEL String Extension Functions Example

This example demonstrates the CEL string extension functions (split(), join(), and format()) that are now supported in cel2sql v3.4.0.

String Extension Functions

split(delimiter [, limit])

Splits a string into an array using a delimiter.

// Basic split (unlimited)
"a,b,c".split(",")              // → STRING_TO_ARRAY('a,b,c', ',')

// Split with limit
"a,b,c,d".split(",", 2)         // → (STRING_TO_ARRAY('a,b,c,d', ','))[1:2]

// Special cases
"text".split(",", 0)            // → ARRAY[]::text[] (empty array)
"text".split(",", 1)            // → ARRAY['text'] (no split)

Parameters:

• delimiter: String delimiter to split on
• limit (optional): Maximum number of splits
  • -1 or omitted: Unlimited splits (default)
  • 0: Return empty array
  • 1: Return original string in array (no split)
  • > 1: Return first N elements

Security: Delimiter cannot contain null bytes.

join([delimiter])

Joins an array into a string using a delimiter.

// Join with delimiter
["a", "b", "c"].join(",")       // → ARRAY_TO_STRING(ARRAY['a', 'b', 'c'], ',', '')

// Join without delimiter (empty string)
["a", "b", "c"].join()          // → ARRAY_TO_STRING(ARRAY['a', 'b', 'c'], '', '')

Parameters:

• delimiter (optional): String to join elements with (default: empty string)

Null Handling: Null elements are replaced with empty strings.

Security: Delimiter cannot contain null bytes.

format(args)

Formats a string using printf-style placeholders.

// Basic formatting
"Hello %s".format(["World"])            // → FORMAT('Hello %s', 'World')

// Multiple arguments
"%s is %d years old".format(["John", 30]) // → FORMAT('%s is %s years old', 'John', 30)

// Escaped percent sign
"100%% complete".format([])             // → FORMAT('100%% complete')

Supported Specifiers:

• %s: String (stays as %s in PostgreSQL)
• %d: Decimal/integer (converted to %s)
• %f: Float (converted to %s)
• %%: Escaped percent sign

Unsupported Specifiers:

• %b, %x, %X, %o, %e, %E, %g, %G

Requirements:

• Format string must be a constant (not dynamic)
• Arguments must be a constant list
• Argument count must match placeholder count

Security:

• Format string limited to 1000 characters
• Only whitelisted specifiers allowed

Running the Example

go run main.go

Example Output

CEL String Extension Functions Examples
==========================================

1. split() - Basic String Splitting
   CEL: person.csv_data.split(',').size() > 0
   SQL: COALESCE(ARRAY_LENGTH(STRING_TO_ARRAY(person.csv_data, ','), 1), 0) > 0
   ✓ Success

2. split() with Limit
   CEL: person.csv_data.split(',', 3).size() == 3
   SQL: COALESCE(ARRAY_LENGTH((STRING_TO_ARRAY(person.csv_data, ','))[1:3], 1), 0) = 3
   ✓ Success

...

Use Cases

1. CSV Parsing and Filtering

// Split CSV, filter non-empty values, rejoin
person.csv_data.split(',').filter(x, x.size() > 0).join('|')

2. Tag Management

// Find specific tag in comma-separated list
person.csv_data.split(',').exists(x, x == 'premium')

// Join tags with custom delimiter
person.tags.join(' | ')

3. Dynamic Message Generation

// Format user-friendly messages
"User %s (age %d) registered with email %s".format([person.name, person.age, person.email])

4. Data Transformation

// Split, transform, and rejoin
person.csv_data.split(',').map(x, x.upperAscii()).join(',')

Integration with Comprehensions

All string extension functions work seamlessly with CEL comprehensions:

// split() in exists
person.csv_data.split(',').exists(x, x == 'target')

// split() in filter
person.csv_data.split(',').filter(x, x.startsWith('a')).size() > 0

// split() in map
person.csv_data.split(',').map(x, x.upperAscii())

// join() with filtered array
person.tags.filter(t, t.startsWith('a')).join(',')

Related Documentation

• CEL String Extensions
• PostgreSQL String Functions
• PostgreSQL Array Functions
• cel2sql Operators Reference

Limitations

split()

• Dynamic limits not supported (must be constant)
• Negative limits other than -1 not supported

join()

• Joins all non-null elements (nulls replaced with empty string)

format()

• Format string must be constant (not dynamic)
• Arguments must be constant list (not dynamic)
• Limited specifier support (%s, %d, %f only)
• No width or precision modifiers

quote()

• Not available (not part of CEL ext.Strings() standard extension)

Security Considerations

All string extension functions include security validations:

• Null Byte Protection: Delimiters cannot contain null bytes
• Format String Validation:
  • Maximum length: 1000 characters
  • Only whitelisted specifiers
  • Argument count validation
• Input Validation: All field names validated for SQL injection

Version History

• v3.4.0: Added split(), join(), and format() support