Constant ordering
There are situations when the order of entities is specified outside evitaDB. The constant order constraints allow to control the order of the selected entities by a caller logic.
The constant ordering constraints are particularly useful when you have a sorted set of unique attributes or directly the entity primary keys provided by an external system that needs to be maintained in the evitaDB output (for example, it represents a relevance of those entities from the full-text engine).
Exact entity primary key order used in filter
The constraint allows output entities to be sorted by primary key values in the exact order used to filter them.
The constraint requires the presence of exactly one entityPrimaryKeyInSet
constraint in the filter part of the query. It uses the specified array of entity primary keys to sort the result
returned by the query.
The sample query returns exactly 4 products, which maintain the order of the filtered primary keys in the query that was issued.
Exact entity primary key order
- argument:int+
a mandatory set of entity primary keys that control the order of the query result
The constraint allows output entities to be sorted by entity primary keys in the exact order specified in the 2nd through Nth arguments of this constraint.
The sample query returns all products whose code starts with the string lenovo, but uses the order of the first three
entities in the output as specified by the order constraint entityPrimaryKeyExact. Because the query returns more
results than the order constraint has information for, the rest of the result set is sorted traditionally by
the entity primary key in ascending order. If there is another order constraint in the chain, it would be used to sort
the rest of the query result.
Exact entity attribute value order used in filter
- argument:string!
- a mandatory name of the attribute name that control the order of the query result
This constraint allows output entities to be sorted by values of the specified attribute in the exact order in which
they were filtered. The constraint requires the presence of exactly one attribute-in-set
in the filter part of the query, referring to the attribute with the same name as used in the first argument of this
constraint. It uses the specified array of attribute values to sort the result returned by the query.
Chain attributes (Predecessor and ReferencedEntityPredecessor) cannot
supply these filter values: they cannot be marked as filterable, so the required
attributeInSet filter is refused. Use
attributeNatural to order by the chain instead.
The sample query returns exactly 3 products, preserving the order of the entity's code attribute used in the filter
constraint of the query that was issued.
Exact entity attribute value order
- argument:string!
- a mandatory name of the attribute name that control the order of the query result
- argument:comparable+
- a mandatory set of attribute values whose data type matches attribute data type, which define the order of the query result
The constraint allows output entities to be sorted by attribute values in the exact order specified in the 2nd through Nth arguments of this constraint.
Chain attributes of type Predecessor or ReferencedEntityPredecessor are
refused when the query is translated, both at entity level and inside
referenceProperty orderings. A chain orders by predecessor links, so its
values cannot be listed in an exact value order. Use attributeNatural to follow
the chain instead. Inside referenceProperty, that needs
traverseByEntityProperty or no traversal constraint at all, because
pickFirstByEntityProperty cannot order by a chain.
Inside a referenceProperty ordering with
traverseByEntityProperty, attributeSetExact orders each block of
the traversal separately (see how the entities are placed). In each
block, the listed values come first, in the listed order, with ties by ascending primary key. An entity whose value
is not listed, or that has no value, passes to the next ordering constraint inside referenceProperty; if none of
them places it, it waits for a later block. Entities that no block places continue to the next ordering constraint of
the query.
The value of an entity is taken from its first reference to the block's entity that has a value - in the order of
the representative attribute values when there are several. A later
reference with a listed value does not replace an earlier one with an unlisted value.
Under pickFirstByEntityProperty, attributeSetExact works only
when the query narrows the ordered reference down to a single referenced entity, for example by filtering for it with
referenceHaving. The same applies to
attributeSetInFilter inside any reference ordering.
The sample query returns all products whose code starts with the string lenovo, but uses the order of the first three
entities in the output as specified by the order constraint attributeSetExact. Because the query returns more
results than the order constraint has information for, the rest of the result set is sorted traditionally by
the entity primary key in ascending order. If there is another order constraint in the chain, it would be used to sort
the rest of the query result.