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Finding Parents by Their Childrenedit
The has_child query and filter can be used to find parent documents based on
the contents of their children. For instance, we could find all branches that
have employees born after 1980 with a query like this:
GET /company/branch/_search
{
"query": {
"has_child": {
"type": "employee",
"query": {
"range": {
"dob": {
"gte": "1980-01-01"
}
}
}
}
}
}
Like the nested query, the has_child query could
match several child documents, each with a different relevance
score. How these scores are reduced to a single score for the parent document
depends on the score_mode parameter. The default setting is none, which
ignores the child scores and assigns a score of 1.0 to the parents, but it
also accepts avg, min, max, and sum.
The following query will return both london and liverpool, but london
will get a better score because Alice Smith is a better match than
Barry Smith:
GET /company/branch/_search
{
"query": {
"has_child": {
"type": "employee",
"score_mode": "max",
"query": {
"match": {
"name": "Alice Smith"
}
}
}
}
}
The default score_mode of none is significantly faster than the other
modes because Elasticsearch doesn’t need to calculate the score for each child
document. Set it to avg, min, max, or sum only if you care about the
score.
min_children and max_childrenedit
The has_child query and filter both accept the min_children and
max_children parameters, which will return the parent document only if the
number of matching children is within the specified range.
This query will match only branches that have at least two employees:
GET /company/branch/_search
{
"query": {
"has_child": {
"type": "employee",
"min_children": 2,
"query": {
"match_all": {}
}
}
}
}
The performance of a has_child query or filter with the min_children or
max_children parameters is much the same as a has_child query with scoring
enabled.