What are the requirements for data validation?

JSON schema supports the following data types:

• array
• boolean
• null
• number
• object
• string

There are several assumptions when building the API schema:

• The value null never occurs by itself in the API. However, fields declared in the API can be nullable.
• It is possible that a field is declared optional. If the JSON passed to the validation does not contain a field declared as optional, then the validation of this field simply does not take place.
• It is possible that a field will take values from 2 or more types (e.g. string | number).

Validation requirements

1. I have to be able to prohibit validation of an object if it contains keys that are not expected.

Validating booleans

Validation of a field of type boolean requires no comment.

Examples of boolean values: true, false.

Validating numbers

I consider the following factors when validating a number field:

• Is it an integer or a float?
• What is the maximum number of digits after the decimal point?
• What is the maximum value?
• What is the minimum value?
• What is the range of values? For example, I may want to validate if a number is between 0 and 10 or 90 and 100.

Examples of number values: -100, -50.555 0, 50.555, 100.

Validating strings

I consider the following factors when validating a string field:

• What is the format of the value? For example, I would like to check formats such as unknown (can be any string), date time, enum, jwt, uuid, email, mobile phone number, url, password, hostname, number, binary (from swagger specification), byte (from swagger specification).
• What is the maximum length of the value?
• What is the minimum length of the value?

Examples of string values: "2022-05-23T12:00:00.000Z", "aa4b72ff-8280-41b8-a3ca-0d6e9cf0f935", "john.doe@gmail.com", "100200300400500600700800900.100200300".

Validating objects

I define an object as a collection of key-value pairs where key names are known in advance.

I consider the following factors when validating an object field:

• Is the key name matching the name I defined it?
• Is the value of a given key matching the schema I declared for that key?

Examples of object values: { foo: "foo" }, { foo: { bar: "bar" } }.

Validating maps

A map is a special type of object in which the key names are unknown.

I consider the following factors when validating a map field:

• Is the key name in the correct type? For example, I want to have a map where keys can be either integers or strings.
• Is the key name included in the key names I allow? For example, I would like the keys in the map to be in cats, dogs or birds only.
• Is the value of a given key matching the schema I declared for that key?

Examples of object values: { foo: "foo", bar: "bar", buzz: "buzz" }.

Validating arrays

I consider the following factors when validating an array field:

• What is the maximum length of the array?
• What is the minimum length of the array?
• What is the schema of elements in the array? For example, I want to have an array of integers between 1 and 10, I want to have an array of objects that match specified schema, I want to have an array of objects that match one of 2 or more specified schemas, I want to have an array of arrays of integers between 1 and 10, I want to have an array of tuples.

Examples of array values: [-5, 0, 0, 0, 5], ["first", "second", "third", "first"], [{ key: "first"}, { key: "second"}, { key: "third"}, { key: "first"}].

Validating sets

Set is a spacial case of array where every single value is unique.

I consider the following factors when validating a set field:

• All considerations for validating arrays.
• Is there any duplicated item?

Examples of set values: [-5, 0, 5], ["first", "second", "third"], [{ key: "first"}, { key: "second"}, { key: "third"}].

Validating tuples

Tuple is a spacial case of array where total number of elements is known upfront and every item has it's own validation rules.

I consider the following factors when validating a set field:

• All considerations for validating arrays.
• Is there any duplicated item?

Examples of tuple values: [1, "first"], ["foo", { bar: "bar" }].

Spacial scenarios

• There is a chance that I will have an endpoint that allows request body to be sent in one of 2 or more declared formats. For example, this commonly occurs while working with webhooks.
• Tree validation is a special case that requires the ability to recursively validate the children of a selected node.

Resources

• A library that provides methods for pagination, sorting, and filtering in the API.
• Official OpenAPI specification.