MongoDB：Graphlookup 嵌套文档仅返回聚合中的单个文档

Question

我正在尝试使用 MongoDB 聚合框架来处理嵌套文档，但无法返回预期的 output，特别是在$graphLookup阶段。 在非嵌套架构中，它会正确查找选项中定义的所有文档并返回所有文档。 但在嵌套的情况下，它只返回一个。 我已经按照这里的回答尝试$unwind和$replaceRoot但现在它不起作用。 通过代码会更容易理解，所以这里是示例。

非嵌套文档（文件fileSystem ）

 db={ "fileSystem": [ { "_id": "a", "label": "Root", "children": [ "b", ], }, { "_id": "b", "label": "Nested folder 1", "children": [ "c", "d", "e" ], "parent": "a" }, { "_id": "c", "label": "Nested File 1.1", "parent": "b" }, { "_id": "d", "label": "Nested File 1.2", "parent": "b" }, ] } // Aggregation Query db.fileSystem.aggregate([ { "$match": { "_id": "a" } }, { "$graphLookup": { "from": "fileSystem", "startWith": "$children", "connectFromField": "children", "connectToField": "_id", "as": "nest", "depthField": "level", "maxDepth": 1 } }, ]) // correct and expected result [ { "_id": "a", "children": [ "b" ], "label": "Root", "nest": [ { "_id": "b", "children": [ "c", "d", "e" ], "label": "Nested folder 1", "level": NumberLong(0), "parent": "a" }, { "_id": "d", "label": "Nested File 1.2", "level": NumberLong(1), "parent": "b" }, { "_id": "c", "label": "Nested File 1.1", "level": NumberLong(1), "parent": "b" } ] } ]

嵌套文档和查询

 db={ "fileSystem": [ { pp: [ { "_id": "a", "label": "Root", "children": [ "b", ], }, //... same as previous ] } ] } // Aggregation Query db.fileSystem.aggregate([ { "$unwind": "$pp" }, { "$replaceRoot": { "newRoot": "$pp" } }, { "$match": { "_id": "a" } }, { "$graphLookup": { "from": "fileSystem", "startWith": "$pp.children", "connectFromField": "pp.children", "connectToField": "pp._id", "as": "nest", "depthField": "level", } }, ]) // incorrect result [ { "_id": "a", "children": [ "b" ], "label": "Root", "nest": [] } ]

预计： https://mongoplayground.net/p/A4yDGUHka58

窃听： https://mongoplayground.net/p/ZlQyDBrYSZr

Answer 1

$graphLookup在from给出的集合中搜索匹配的文档。 它使用管道中的每个文档作为起点，但它不搜索，也不会从管道返回文档。

在示例数据中，只有 1 个文档，因此在这种情况下，您最好让next数组包含原始文档。

操场