#Schema validation

#Description

JSON Schema is a vocabulary for annotating and validating data in JavaScript. More about JSON Schema on json-schema.org

A schema can be used from the simplest description of the data type of a value:

{
  type: "string"
}

"Foo"

To an object with both rules for required fields and validation rules for single values:

{
  type: "object",
  properties: {
    txt: { type: 'string', minLength: 5 },
    num: { type: 'number', maximum: 100 },
  },
  required: ['txt']
}

{
  "txt": "abcde",
  "num": 123
}

#Using schema with DataContext

Since a DataContext (used in isolation or through the use of Form.Handler) supports JSON Schema, these two examples will result in the same validation for the user:

<Form.Handler data={user}>
  <Field.String path="/name" label="Name" minLength={3} required />
  <Field.Email path="/email" label="E-mail" required />
  <Field.Number
    path="/birthyear"
    label="Birth year"
    minimum={1900}
    maximum={2023}
    required
  />
</Form.Handler>

const schema = {
  type: 'object',
  properties: {
    name: { type: 'string', minLength: 3 },
    email: { type: 'string' },
    birthyear: { type: 'number', minimum: 1900, maximum: 2023 }
  },
  required: ['name', 'email', 'birthyear'],
}
<Form.Handler data={user} schema={schema}>
  <Field.String path="/name" label="Name"  />
  <Field.Email path="/email" label="E-mail" />
  <Field.Number path="/birthyear" label="Birth year" />
</Form.Handler>

This makes it possible to create a uniform, testable description and requirements specification for the data, which can be tested independently of frontend code, and used across systems, e.g. frontend and backend.

#Complex schemas

In addition to basic validation as in the example above, JSON Schema can be used for more complex. Examples of definitions supported by the standard are:

• Requirement that the object must not have other properties than those defined in properties.
• Nested data structures and combinations of objects and arrays with rules for array elements (fixed or repetitive elements).
• Regular expressions for the syntax of individual values.
• Enum (a set of valid values).
• Rules for the number of elements in arrays.
• Rules for the number of properties in objects.
• Predefined format rules (eg 'uri', 'email' and 'hostname').
• Logical operators such as 'not', 'oneOf', 'allOf' and 'anyOf' which can be filled with rules for all or part of the data set.
• Rule set based on the content of values (if-then-else).
• Rules (sub-schemas) that become applicable if a given value is present.
• Reuse within the definition, such as one and the same object structure being used as a definition for several locations in a structure.

To learn more about what is possible with the JSON Schema standard, see json-schema.org.