elasticsearch parent/child query logic - elasticsearch

Question

elastic version: 5.0.1
define mapping：
PUT test
{
"mappings": {
"my_parent": {
"properties": {
"key": {
"type": "keyword"
}
}
},
"my_child": {
"_parent": {
"type": "my_parent"
},
"properties": {
"key": {
"type": "keyword"
}
}
}
}
}
add demo data:
POST _bulk
{"update": {"_index": "test","_type": "my_parent","_id": "1"}}
{"doc": {"key": 1},"doc_as_upsert": true}
{"update": {"_index": "test","_type": "my_child","_parent": 1,"_id": "11"}}
{"doc": {"key": 11},"doc_as_upsert": true}
{"update": {"_index": "test","_type": "my_child","_parent": 1,"_id": "12"}}
{"doc": {"key": 12},"doc_as_upsert": true}
query:
POST test/my_parent/_search
{
"query": {
"bool": {
"filter": {
"bool": {
"should": [
{
"bool": {
"must": [
{
"term": {
"key": 3
}
},
{
"has_child": {
"type": "my_child",
"inner_hits": {
"name": "a"
},
"query": {
"term": {
"key": 11
}
}
}
}
]
}
},
{
"has_child": {
"type": "my_child",
"inner_hits": {
"name": "b"
},
"query": {
"term": {
"key": 12
}
}
}
}
]
}
}
}
}
}
result:
{
"took": 2,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0,
"hits": [
{
"_index": "test",
"_type": "my_parent",
"_id": "1",
"_score": 0,
"_source": {
"key": 1
},
"inner_hits": {
"a": {
"hits": {
"total": 1,
"max_score": 0.9808292,
"hits": [
{
"_type": "my_child",
"_id": "11",
"_score": 0.9808292,
"_routing": "1",
"_parent": "1",
"_source": {
"key": 11
}
}
]
}
},
"b": {
"hits": {
"total": 1,
"max_score": 0.9808292,
"hits": [
{
"_type": "my_child",
"_id": "12",
"_score": 0.9808292,
"_routing": "1",
"_parent": "1",
"_source": {
"key": 12
}
}
]
}
}
}
}
]
}
}
question here:
Do 'must'\'should'\'must_not' clause have the same meaning between plain search and parent\child search?
Why the result of inner_hits with name 'a' is returned?

Answer 1

'must'|'should'|'must_not' clauses have different meaning. Let me explain you with example of the plain search.
Understand these clause with equivalent SQL query.
must: The clause (query) must appear in matching documents and will contribute to the score.
SQL: select * from user where country_code = 'US' AND state_code = 'NY'
Query DSL:
POST _search
{
"query": {
"bool": {
"must": [
{"term": {"country_code": "US"}},
{"term": {"state_code": "NY"}}
]
}
}
}
should: At least one of these clauses must match, like logical OR.
SQL: select * from user where country_code = 'US' OR state_code = 'NY'
Query DSL:
POST _search
{
"query": {
"bool": {
"should": [
{"term": {"country_code": "US"}},
{"term": {"state_code": "NY"}}
]
}
}
}
must_not: Condition must not match the documents.
SQL: select * from user where country_code != 'US' AND state_code != 'NY'
Query DSL:
POST _search
{
"query": {
"bool": {
"must_not": [
{"term": {"country_code": "US"}},
{"term": {"state_code": "NY"}}
]
}
}
}
Why the result of inner_hits with name 'a' is returned?
Because you put two has_child condition inside the should filter. As explain above it is matching the document from (inner_hits.name =a ..) OR ( inner_hits.name=b ..)