Pass and fail examples¶

Each example below was run through the checker. The comment at the top of each contract is the exact result it reports. The examples follow the rule in Missing vs null values:

Key missing (no line for it): only required fails. Every other check is skipped and adds no result to the report.
Key left blank (owner: with nothing after it): every check fails with Attribute '<path>' is null.
Blank item (a - with nothing after it, or a blank entry under fields:): fails with contains N null element(s) and isn't counted by min_items / max_items.

Empty values such as "" or [] are not blank: they count as filled in.

`required`¶

required: true fails when the key is missing or left blank. It is the only check that looks at whether a key exists.

data_contract_checks:
  - attribute: info.owner
    checks:
      - required: true

PassesFails

# Owner filled in
#   PASS: Attribute 'info.owner' is present
info:
  title: Orders
  owner: alice
---
# Owner is an empty string
#   PASS: Attribute 'info.owner' is present
info:
  title: Orders
  owner: ""

# Owner line missing
#   FAIL: Required attribute 'info.owner' is missing
info:
  title: Orders
---
# Owner left blank
#   FAIL: Required attribute 'info.owner' is null
info:
  title: Orders
  owner:

required: false adds nothing to the report, whatever the contract holds. Write it only to document that a field is optional.

data_contract_checks:
  - attribute: info.owner
    checks:
      - required: false

Skipped

# Owner filled in
#   (no result)
info:
  title: Orders
  owner: alice
---
# Owner line missing
#   (no result)
info:
  title: Orders
---
# Owner left blank
#   (no result)
info:
  title: Orders
  owner:

`pattern`¶

pattern fails a value that doesn't match the regular expression, or a key left blank. It skips a missing key.

data_contract_checks:
  - attribute: info.owner
    checks:
      - pattern: ^[a-z]+$

PassesFailsSkipped

# Lowercase owner
#   PASS: Attribute 'info.owner' value 'alice' matches pattern '^[a-z]+$'
info:
  title: Orders
  owner: alice

# Capitalised owner
#   FAIL: Attribute 'info.owner' value 'Alice' does not match pattern '^[a-z]+$'
info:
  title: Orders
  owner: Alice
---
# Owner left blank
#   FAIL: Attribute 'info.owner' is null
info:
  title: Orders
  owner:

# Owner line missing
#   (no result)
info:
  title: Orders

`accepted_values`¶

accepted_values fails a value that isn't in the list, a key left blank, or a blank item in a list. A list gets one result per item.

Values are compared with the type the contract specification gives the field. DCS types pii as a boolean, so the config uses an unquoted false:

data_contract_checks:
  - attribute: models.*.fields.*.pii
    checks:
      - accepted_values: [false]   # no field may contain PII

A quoted "false" is a string and never matches the boolean false, the same way --lint rejects pii: "false" in a contract. A failure caused by quotes says so in its message. Numbers match by value, so 1 and 1.0 are the same.

Dates and timestamps are strings in every supported specification, so both the contract and the checks config keep them as the text that was written, quoted or not: accepted_values: [2024-01-01T00:00:00Z] matches a contract contractCreatedTs: 2024-01-01T00:00:00Z.

data_contract_checks:
  - attribute: info.env
    checks:
      - accepted_values:
          - prod
          - dev

PassesFailsSkipped

# Allowed value
#   PASS: Attribute 'info.env' value 'prod' is in the list of accepted values
info:
  title: Orders
  env: prod
---
# List of allowed values
#   PASS: Attribute 'info.env' value 'prod' is in the list of accepted values
#   PASS: Attribute 'info.env' value 'dev' is in the list of accepted values
info:
  title: Orders
  env:
    - prod
    - dev

# Value not in the list
#   FAIL: Attribute 'info.env' value 'test' is not in the list of accepted values: '['prod', 'dev']'
info:
  title: Orders
  env: test
---
# List with one bad value
#   PASS: Attribute 'info.env' value 'prod' is in the list of accepted values
#   FAIL: Attribute 'info.env' value 'test' is not in the list of accepted values: '['prod', 'dev']'
info:
  title: Orders
  env:
    - prod
    - test
---
# Env left blank
#   FAIL: Attribute 'info.env' is null
info:
  title: Orders
  env:
---
# List with an empty item
#   FAIL: Attribute 'info.env' contains 1 null element(s)
#   PASS: Attribute 'info.env' value 'prod' is in the list of accepted values
info:
  title: Orders
  env:
    - prod
    -

# Env line missing
#   (no result)
info:
  title: Orders

`min_items`¶

min_items fails a list with too few items, a key left blank, or a blank item in the list. Blank items are not counted.

data_contract_checks:
  - attribute: info.tags
    checks:
      - min_items: 2

PassesFailsSkipped

# Two tags
#   PASS: Attribute 'info.tags' has at least 2 items
info:
  title: Orders
  tags:
    - orders
    - sales

# One tag
#   FAIL: Attribute 'info.tags' has fewer than 2 items
info:
  title: Orders
  tags:
    - orders
---
# Empty list
#   FAIL: Attribute 'info.tags' has fewer than 2 items
info:
  title: Orders
  tags: []
---
# Tags left blank
#   FAIL: Attribute 'info.tags' is null
info:
  title: Orders
  tags:
---
# One tag plus an empty item
#   FAIL: Attribute 'info.tags' contains 1 null element(s)
#   FAIL: Attribute 'info.tags' has fewer than 2 items
info:
  title: Orders
  tags:
    - orders
    -
---
# Two tags plus an empty item
#   FAIL: Attribute 'info.tags' contains 1 null element(s)
#   PASS: Attribute 'info.tags' has at least 2 items
info:
  title: Orders
  tags:
    - orders
    - sales
    -

# Tags line missing
#   (no result)
info:
  title: Orders

`max_items`¶

max_items fails a list with too many items, a key left blank, or a blank item in the list. Blank items are not counted.

data_contract_checks:
  - attribute: info.tags
    checks:
      - max_items: 2

PassesFailsSkipped

# Two tags
#   PASS: Attribute 'info.tags' has at most 2 items
info:
  title: Orders
  tags:
    - orders
    - sales

# Three tags
#   FAIL: Attribute 'info.tags' has more than 2 items
info:
  title: Orders
  tags:
    - orders
    - sales
    - finance
---
# Tags left blank
#   FAIL: Attribute 'info.tags' is null
info:
  title: Orders
  tags:
---
# Two tags plus an empty item
#   FAIL: Attribute 'info.tags' contains 1 null element(s)
#   PASS: Attribute 'info.tags' has at most 2 items
info:
  title: Orders
  tags:
    - orders
    - sales
    -

# Tags line missing
#   (no result)
info:
  title: Orders

`at_least_one`¶

at_least_one fails when no field matches, when fields: is left blank, or when a field under it is left blank. Point it at the collection; it runs once per model.

data_contract_checks:
  - attribute: models.*.fields
    checks:
      - at_least_one:
          primaryKey: true

PassesFailsSkipped

# One primary key
#   PASS: Attribute 'models.orders.fields' contains at least one item with 'primaryKey: True'
models:
  orders:
    fields:
      order_id:
        type: text
        primaryKey: true
      amount:
        type: decimal
---
# Two primary keys
#   PASS: Attribute 'models.orders.fields' contains at least one item with 'primaryKey: True'
models:
  orders:
    fields:
      order_id:
        primaryKey: true
      customer_id:
        primaryKey: true

# No primary key
#   FAIL: Attribute 'models.orders.fields' has no items with 'primaryKey: True'
models:
  orders:
    fields:
      order_id:
        type: text
      amount:
        type: decimal
---
# Fields left blank
#   FAIL: Attribute 'models.orders.fields' is null
models:
  orders:
    description: All orders
    fields:
---
# A field left blank
#   FAIL: Attribute 'models.orders.fields' contains 1 null element(s): amount
#   PASS: Attribute 'models.orders.fields' contains at least one item with 'primaryKey: True'
models:
  orders:
    fields:
      order_id:
        primaryKey: true
      amount:

# Fields line missing
#   (no result)
models:
  orders:
    description: All orders

`exactly_one`¶

exactly_one fails when zero, or two or more, fields match, when fields: is left blank, or when a field under it is left blank. Point it at the collection; it runs once per model.

data_contract_checks:
  - attribute: models.*.fields
    checks:
      - exactly_one:
          primaryKey: true

PassesFailsSkipped

# One primary key
#   PASS: Attribute 'models.orders.fields' contains exactly one item with 'primaryKey: True'
models:
  orders:
    fields:
      order_id:
        type: text
        primaryKey: true
      amount:
        type: decimal

# Two primary keys
#   FAIL: Attribute 'models.orders.fields' has 2 items with 'primaryKey: True', expected exactly 1
models:
  orders:
    fields:
      order_id:
        primaryKey: true
      customer_id:
        primaryKey: true
---
# No primary key
#   FAIL: Attribute 'models.orders.fields' has 0 items with 'primaryKey: True', expected exactly 1
models:
  orders:
    fields:
      order_id:
        type: text
      amount:
        type: decimal
---
# Fields left blank
#   FAIL: Attribute 'models.orders.fields' is null
models:
  orders:
    description: All orders
    fields:
---
# A field left blank
#   FAIL: Attribute 'models.orders.fields' contains 1 null element(s): amount
#   PASS: Attribute 'models.orders.fields' contains exactly one item with 'primaryKey: True'
models:
  orders:
    fields:
      order_id:
        primaryKey: true
      amount:

# Fields line missing
#   (no result)
models:
  orders:
    description: All orders

Pass and fail examples¶

required¶

pattern¶

accepted_values¶

min_items¶

max_items¶

at_least_one¶

exactly_one¶

`required`¶

`pattern`¶

`accepted_values`¶

`min_items`¶

`max_items`¶

`at_least_one`¶

`exactly_one`¶