有没有办法返回Google Cloud Datastore中没有后代的实体?
If your question is if you can retrieve an entity that has no descendants, then yes. You can retrieve any entity through their key (or through a query).
However, if you intend to run a query that retrieves all the child-less entities, this will not be possible. The ancestry information is stored in the descendant entities, so you should recover all the ancestor keys for all the entities (through a projection query ), store all the keys for their ancestors, and then run a query for all the entities checking those that are not ancestors to any entity.
Using curl and jq in a shell, it could be something like the following:
export ancestors=$(gcurl -s -H'content-type:application/json' "https://datastore.googleapis.com/v1/projects/$(gcloud config get-value project):runQuery?fields=batch%2FentityResults%2Fentity%2Fkey%2Fpath" -d"{
\"partitionId\": {
\"projectId\": \"$(gcloud config get-value project)\",
\"namespaceId\": \"namespace_id\"
},
\"query\": {
\"kind\": [
{
\"name\": \"descendant_entity_name\"
}
],
\"projection\": [
{
\"property\": {
\"name\": \"__key__\"
}
}
]
}
}" | jq '[.batch.entityResults[].entity.key.path | select(length > 1 ) | .[-2].id]')
gcurl -H'content-type:application/json' "https://datastore.googleapis.com/v1/projects/$(gcloud config get-value project):runQuery?fields=batch%2FentityResults%2Fentity%2Fkey%2Fpath" -d"{
\"partitionId\": {
\"projectId\": \"$(gcloud config get-value project)\",
\"namespaceId\": \"namespace_id\"
},
\"query\": {
\"kind\": [
{
\"name\": \"ancestor_entity_name\"
}
],
\"projection\": [
{
\"property\": {
\"name\": \"__key__\"
}
}
]
}
}" | jq '.batch.entityResults[].entity.key.path[-1].id | select(inside(env.ancestors)|not)'
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