mongodb聚合-将数组的内容设置为输入，同时存储同级键

通过此新 MongoPlayground链接获取测试数据.检查从链接获取的更新查询: db.Forests.aggregate([{$ unwind:" $ forests"}，{$ unwind:" $ forests.trees"}，{$ unwind:"$ forests.trees.branches"}，{$ lookup:{来自:叶子"，localField:"forests.trees.branches.branch_id"，foreignField:"branch_id"，如:"forests.trees.branches.leaves"；}}，{$ addFields:{"forests.trees.branches.leaf_count":{$ size:"$ forests.trees.branches.leaves"}}}，{$ project:{" forests.trees.branches.leaves" ;: 0}}，{$ group:{_ID: {forest_id:"$ forests.forest_id"，tree_id:" $ forests.trees.tree_id"}，forest_ranger:{$ first:" $ forest_ranger"}，some_other_data:{$ first:" $ some_other_data"}，leaf_count:{$ sum:"$ forests.trees.branches.leaf_count"}，分支机构:{$ push:" $ forests.trees.branches"}}}，{$ group:{_id:"$ _ id.forest_id"，forest_ranger:{$ first:" $ forest_ranger"}，some_other_data:{$ first:" $ some_other_data"}，leaf_count:{$ sum:"$ leaf_count"；}，树木:{$ push:{leaf_count:{$ sum:"$ leaf_count"；}，tree_id:"$ _ id.tree_id"，分支机构:"$ branches"}}}}，{$ group:{_id:null，forest_ranger:{$ first:" $ forest_ranger"}，some_other_data:{$ first:" $ some_other_data"}，leaf_count:{$ sum:"$ leaf_count"；}，森林:{$ push:{leaf_count:{$ sum:"$ leaf_count"；}，forest_id:"$ _ id"，树:"$ trees"}}}}，{$ project:{_id:0}}]) 输出: {"forest_ranger":"bob"，" some_other_data":{数据":虚拟数据"；}，"leaf_count"；:4森林":[{"leaf_count"；:3"forest_id":"forestA"，树":[{"leaf_count"；:1"tree_id":"treeB"，分支":[{"branch_id":"branchB"，"leaf_count"；:1}]}，{"leaf_count"；:2"tree_id":"treeA"，分支":[{"branch_id":"branchA"，"leaf_count"；:1}，{"branch_id":"branchA1"，"leaf_count"；:1}，{"branch_id":"branchA2"，"leaf_count"；:0}]}]}，{"leaf_count"；:1"forest_id":"forestB"，树":[{"leaf_count"；:0，"tree_id":"treeD"，分支":[{"branch_id":"branchD"，"leaf_count"；:0}]}，{"leaf_count"；:1"tree_id":"treeC"，分支":[{"branch_id":"branchC"，"leaf_count"；:1}]}]}，{"leaf_count"；:0，"forest_id":"forestC"，树":[{"leaf_count"；:0，"tree_id":"treeE"，分支":[{"branch_id":"branchE"，"leaf_count"；:0}]}]}]} I'm in the middle of an aggregation pipeline when I have the following data passed from the previous step as input to a "count all leaves in all branches/trees/forests" as indicated in this question: Need guidance on mongo aggregate lookup to count subnodes in all child nodes for each node{ forest_ranger: "bob", some_other_data: {}, forests: [ { forest_id: 'forestA', trees: [ { tree_id: 'treeA', branches: [ { branch_id: 'branchA', } ] } ] } ],}I have that all working properly, but only if I'm reading directly from a collection.My question is - how can Ia) save forest_ranger and some_other_data "for later"b) and start the next stage by mapping forests as the array of documents that are input to the "count all leaves"?Note - I tried to get just (b) working for starters, but I can't seem to treat "forests" as an array so that the solution in the link above can do its magic.Then- when that phase is done, extract what was stored in (a) to get the original format back with all the counts. 解决方案 That is the main disadvantage of using $group. You have to explicitly carry forward every non participating fields using either $first or $last like this:Get the test data with those additional fields from this new MongoPlayground link.Check the updated query taken from the link:db.Forests.aggregate([ { $unwind: "$forests" }, { $unwind: "$forests.trees" }, { $unwind: "$forests.trees.branches" }, { $lookup: { from: "Leaves", localField: "forests.trees.branches.branch_id", foreignField: "branch_id", as: "forests.trees.branches.leaves" } }, { $addFields: { "forests.trees.branches.leaf_count": { $size: "$forests.trees.branches.leaves" } } }, { $project: { "forests.trees.branches.leaves": 0 } }, { $group: { _id: { forest_id: "$forests.forest_id", tree_id: "$forests.trees.tree_id" }, forest_ranger: { $first: "$forest_ranger" }, some_other_data: { $first: "$some_other_data" }, leaf_count: { $sum: "$forests.trees.branches.leaf_count" }, branches: { $push: "$forests.trees.branches" } } }, { $group: { _id: "$_id.forest_id", forest_ranger: { $first: "$forest_ranger" }, some_other_data: { $first: "$some_other_data" }, leaf_count: { $sum: "$leaf_count" }, trees: { $push: { leaf_count: { $sum: "$leaf_count" }, tree_id: "$_id.tree_id", branches: "$branches" } } } }, { $group: { _id: null, forest_ranger: { $first: "$forest_ranger" }, some_other_data: { $first: "$some_other_data" }, leaf_count: { $sum: "$leaf_count" }, forests: { $push: { leaf_count: { $sum: "$leaf_count" }, forest_id: "$_id", trees: "$trees" } } } }, { $project: { _id: 0 } }])Output:{ "forest_ranger" : "bob", "some_other_data" : { "data" : "Dummy data" }, "leaf_count" : 4, "forests" : [ { "leaf_count" : 3, "forest_id" : "forestA", "trees" : [ { "leaf_count" : 1, "tree_id" : "treeB", "branches" : [ { "branch_id" : "branchB", "leaf_count" : 1 } ] }, { "leaf_count" : 2, "tree_id" : "treeA", "branches" : [ { "branch_id" : "branchA", "leaf_count" : 1 }, { "branch_id" : "branchA1", "leaf_count" : 1 }, { "branch_id" : "branchA2", "leaf_count" : 0 } ] } ] }, { "leaf_count" : 1, "forest_id" : "forestB", "trees" : [ { "leaf_count" : 0, "tree_id" : "treeD", "branches" : [ { "branch_id" : "branchD", "leaf_count" : 0 } ] }, { "leaf_count" : 1, "tree_id" : "treeC", "branches" : [ { "branch_id" : "branchC", "leaf_count" : 1 } ] } ] }, { "leaf_count" : 0, "forest_id" : "forestC", "trees" : [ { "leaf_count" : 0, "tree_id" : "treeE", "branches" : [ { "branch_id" : "branchE", "leaf_count" : 0 } ] } ] } ]} 这篇关于mongodb聚合-将数组的内容设置为输入，同时存储同级键的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！