mirror of https://gitee.com/bigwinds/arangodb
44 lines
2.1 KiB
Markdown
44 lines
2.1 KiB
Markdown
Multiple Path Search
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====================
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The shortest path algorithm can only determine one shortest path.
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For example, if this is the full graph (based on the [mps_graph](../../Manual/Graphs/index.html#the-mps-graph)):
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then a shortest path query from **A** to **C** may return the path `A -> B -> C` or `A -> D -> C`, but it's undefined which one (not taking edge weights into account here).
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You can use the efficient shortest path algorithm however, to determine the shortest path length:
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@startDocuBlockInline GRAPHTRAV_multiplePathSearch
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@EXAMPLE_AQL{GRAPHTRAV_multiplePathSearch}
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@DATASET{mps_graph}
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RETURN LENGTH(
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FOR v IN OUTBOUND
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SHORTEST_PATH "mps_verts/A" TO "mps_verts/C" mps_edges
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RETURN v
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)
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@END_EXAMPLE_AQL
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@endDocuBlock GRAPHTRAV_multiplePathSearch
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The result is 3 for the example graph (includes the start vertex). Now, subtract 1 to get the edge count / traversal depth. You can run a pattern matching traversal to find all paths with this length (or longer ones by increasing the min and max depth). Starting point is **A** again, and a filter on the document ID of v (or p.vertices[-1]) ensures that we only retrieve paths that end at point **C**.
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The following query returns all parts with length 2, start vertex **A** and target vertex **C**:
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@startDocuBlockInline GRAPHTRAV_multiplePathSearch2
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@EXAMPLE_AQL{GRAPHTRAV_multiplePathSearch2}
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@DATASET{mps_graph}
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FOR v, e, p IN 2..2 OUTBOUND "mps_verts/A" mps_edges
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FILTER v._id == "mps_verts/C"
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RETURN CONCAT_SEPARATOR(" -> ", p.vertices[*]._key)
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@END_EXAMPLE_AQL
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@endDocuBlock GRAPHTRAV_multiplePathSearch2
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A traversal depth of `3..3` would return `A -> E -> F -> C` and `2..3` all three paths.
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Note that two separate queries are required to compute the shortest path length and to do the pattern matching based on the shortest path length (minus 1), because min and max depth can't be expressions (they have to be known in advance, so either be number literals or bind parameters).
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