CQL (Cardinal Query Language) is a simple query language that provides an easy way to access the game state without having to write a custom Query.

You can use it by making a POST request to the /query/game/cql with the CQL query. See the REST API documentation for more information.

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Querying Entities

CQL allows you to use the name of Components to specify the entities you want to query in Cardinal.

For example, let’s say you have the following component definition:

package component

type Health struct {
    Current int
    Max int
}

func (Health) Name() string {
    return "Health"
}

type Attack struct {
    Damage int
}

func (Attack) Name() string {
    return "Attack"
}

You can query all entities that have a health and attack component by using the following query:

CONTAINS(Health, Attack)

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Functions

Two functions are provided in the language that accept a variadic amount of components as parameters: EXACT(…) and CONTAINS(…)

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EXACT(…)

EXACT is a query for entities that contain “exactly” the specified the components. Nothing more nothing less.

Examples:

• EXACT(healthComponent) is a query for all entities with exactly one health component; nothing more.
• EXACT(healthComponent, attackComponent) is a query for all entities with exactly one health component and one attack component; nothing more.

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CONTAINS(…)

CONTAINS is a query for entities that only need to “contain” the specified components. If an entity has more components than just the specified component(s), it is still a valid entity for that query.

Examples:

• CONTAINS(armComponent) is a query for all entities that have an arm component. The entity can have more components than just the arm.
• CONTAINS(armComponent, legComponent) is query for all entities that have both an arm component and a leg component. The entity can have more components than the arm and the leg.

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Logical Operators

CQL provides three logical operators: ! (not), & (and), and | (or).

NOT (!)

! negates a query.

• Example: !CONTAINS(healthComponent) queries all entities that do not contain a health component.

AND (&)

& performs the “and” operation on two queries.

• Example: CONTAINS(healthComponent) & !CONTAINS(attackComponent) is a query for all entities that contain a health component “and” does not contain an attack component

OR (|)

| performs the “or” operation on two queries.

• Example: CONTAINS(healthComponent) | !CONTAINS(attackComponent) is a query for all entities that either contains a health component “or” does not contain an attack component

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Operator Precedence

Operators in CQL do not have any intrinsic precedence. All expressions are consumed from left to right.

• Example: A & B | C & D | F is equivalent to ( ( A & B ) | C ) & D ) | F)

You can use parenthesis to specify and change precedence in CQL.

• Example: EXACT(legComponent) | (!CONTAINS(healthComponent) & !CONTAINS(attackComponent))

• The above is a query for either an entity with only a leg component or an entity that does not have a health component and also does not have an attack component.

• Example: (EXACT(legComponent) | !CONTAINS(healthComponent)) & !CONTAINS(attackComponent)

• The above is the same query but with precedence changed. Now it is querying an entity with either exactly one leg component or does not have a health component. Additionally that entity must not ever contain an attack component.