如何执行排除空连接的graphLookUp？

Question

我需要在可空字段上执行graphLookUp。在本例中，我有一个“节点”集合，其中"name“和"connectsTo”可能都为空，但如果它们都为空，则不应将其视为有效连接：

{ _id: 1, name: "1", connectsTo: null }
{ _id: 2, name: "2", connectsTo: "1" }
{ _id: 3, name: "3", connectsTo: "2" }
{ _id: 4, name: null, connectsTo: "3" }
{ _id: 5, name: null, connectsTo: "3" }
{ _id: 6, name: "6", connectsTo: null }
{ _id: 7, name: null, connectsTo: "6" }

这张图是这样的：

1 <- 2 <- 3 <- 4
            <- 5
6 <- 7

4、5和7都有空名。

我希望从1得到节点的层次结构，并排除从1断开连接的任何节点。

我尝试过这样的查询：

db.nodes.aggregate([
  { $match: { _id: 1 } },
  { $graphLookup: {
      from: "nodes",
      startWith: "$name",
      connectFromField: "name",
      connectToField: "connectsTo",
      as: "hierarchy",
      depthField: "depth"
  }}
]).pretty()

然而，这产生了以下结果：

{
    "_id" : 1,
    "name" : "1",
    "connectsTo" : null,
    "hierarchy" : [
        { "_id" : 7, "name" : null, "connectsTo" : "6",  "depth" : NumberLong(4) },
        { "_id" : 1, "name" : "1",  "connectsTo" : null, "depth" : NumberLong(3) },
        { "_id" : 6, "name" : "6",  "connectsTo" : null, "depth" : NumberLong(3) },
        { "_id" : 5, "name" : null, "connectsTo" : "3",  "depth" : NumberLong(2) },
        { "_id" : 4, "name" : null, "connectsTo" : "3",  "depth" : NumberLong(2) },
        { "_id" : 3, "name" : "3",  "connectsTo" : "2",  "depth" : NumberLong(1) },
        { "_id" : 2, "name" : "2",  "connectsTo" : "1",  "depth" : NumberLong(0) }
    ]
}

如你所见，7和6都存在。我怀疑发生的情况是，6的空connectsTo正与空名称4或5匹配。

如何在名称为null的节点之后立即终止层次结构？

Answer 1

答案是使用restrictSearchWithMatch并排除connectsTo不为空的地方。由于这会在与节点匹配时终止递归，这就排除了6(它有一个空connectsTo)，然后也排除了7，因为7现在与图断开连接：

db.nodes.aggregate([
  { $match: { _id: 1 } },
  { $graphLookup: {
      from: "nodes",
      startWith: "$name",
      connectFromField: "name",
      connectToField: "connectsTo",
      as: "hierarchy",
      depthField: "depth"
      restrictSearchWithMatch: {
        connectsTo: { $ne: null }
      }
  }}
]).pretty()