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String Functions

Vague provides built-in functions for string manipulation and transformation.

Case Transformations​

uppercase / lowercase​

schema Text {
  name: "Hello World",

  upper: uppercase(name),   // "HELLO WORLD"
  lower: lowercase(name)    // "hello world"
}

capitalize​

Title case transformation:

schema Text {
  raw: "hello world",
  title: capitalize(raw)    // "Hello World"
}

Case Style Conversions​

kebabCase​

schema Slug {
  title: "Hello World",
  slug: kebabCase(title)    // "hello-world"
}

snakeCase​

schema Python {
  name: "Hello World",
  var: snakeCase(name)      // "hello_world"
}

camelCase​

schema JavaScript {
  name: "hello world",
  prop: camelCase(name)     // "helloWorld"
}

String Manipulation​

trim​

Remove leading/trailing whitespace:

schema Clean {
  raw: "  hello  ",
  trimmed: trim(raw)        // "hello"
}

concat​

Join strings together:

schema User {
  first: firstName(),
  last: lastName(),

  full: concat(first, " ", last),     // "John Smith"
  email: concat(lowercase(first), ".", lowercase(last), "@example.com")
}

substring​

Extract part of a string:

schema Excerpt {
  text: sentence(),

  // substring(string, start, length)
  first5: substring(text, 0, 5),
  middle: substring(text, 5, 10)
}

replace​

Replace occurrences:

schema Sanitize {
  raw: "hello-world",

  // replace(string, find, replacement)
  clean: replace(raw, "-", "_")   // "hello_world"
}

length​

Get string length:

schema Stats {
  text: sentence(),
  chars: length(text)
}

Practical Examples​

User Profile​

schema User {
  first_name: firstName(),
  last_name: lastName(),

  // Display name
  display_name: concat(first_name, " ", last_name),

  // Username (lowercase, dot-separated)
  username: lowercase(concat(first_name, ".", last_name)),

  // Initials
  initials: concat(
    substring(first_name, 0, 1),
    substring(last_name, 0, 1)
  ),

  // URL slug
  profile_slug: kebabCase(concat(first_name, " ", last_name))
}

Product Catalog​

schema Product {
  name: faker.commerce.productName(),

  // URL-friendly slug
  slug: kebabCase(name),

  // Search-friendly
  search_name: lowercase(name),

  // SKU from name
  sku: concat(
    uppercase(substring(name, 0, 3)),
    "-",
    regex("[0-9]{4}")
  )
}

Content Processing​

schema Article {
  title: faker.lorem.sentence(),
  body: faker.lorem.paragraphs(),

  // URL slug
  slug: kebabCase(title),

  // Meta description (first 160 chars)
  meta_description: substring(body, 0, 160),

  // Word count approximation
  char_count: length(body)
}

Code Generation​

schema APIEndpoint {
  resource: "User" | "Product" | "Order",

  // REST endpoint
  path: concat("/api/", kebabCase(resource), "s"),

  // Database table
  table_name: snakeCase(resource),

  // TypeScript interface
  interface_name: concat("I", resource),

  // Service class
  service_name: concat(resource, "Service")
}

Data Normalization​

schema Contact {
  raw_name: "  JOHN   SMITH  ",
  raw_email: "John.Smith@EXAMPLE.com",

  // Normalized name
  name: capitalize(trim(lowercase(raw_name))),

  // Normalized email
  email: lowercase(trim(raw_email))
}

Chaining Functions​

String functions can be chained:

schema Complex {
  input: "  Hello World  ",

  processed: kebabCase(trim(lowercase(input)))
  // Result: "hello-world"
}

Function Reference​

FunctionDescriptionExample
uppercase(s)Convert to uppercase"HELLO"
lowercase(s)Convert to lowercase"hello"
capitalize(s)Title case"Hello World"
kebabCase(s)Kebab case"hello-world"
snakeCase(s)Snake case"hello_world"
camelCase(s)Camel case"helloWorld"
trim(s)Remove whitespace"hello"
concat(a, b, ...)Join strings"ab"
substring(s, start, len)Extract substring"hel"
replace(s, find, repl)Replace text"hi"
length(s)String length5