TestUtils: copy single node (#252)

core/src/main/scala/flatgraph/Accessors.scala

@@ -162,14 +162,20 @@ object Accessors {
     new ISeq(vals, qty(seq), qty(seq + 1))
   }
 
-  def getNodeProperties(node: GNode): IterableOnce[(String, IndexedSeq[Any])] = {
+  def _getNodeProperties(node: GNode): IterableOnce[(Int, IndexedSeq[Any])] = {
     val schema = node.graph.schema
     for {
       propertyKind <- schema.propertyKinds
       property = Accessors.getNodeProperty(node, propertyKind)
       if property.nonEmpty
-      propertyLabel = schema.getPropertyLabel(node.nodeKind, propertyKind)
-    } yield propertyLabel -> property
+    } yield propertyKind -> property
+  }
+
+  def getNodeProperties(node: GNode): IterableOnce[(String, IndexedSeq[Any])] = {
+    for {
+      (propertyKind, value) <- _getNodeProperties(node)
+      schema = node.graph.schema
+    } yield schema.getPropertyLabel(node.nodeKind, propertyKind) -> value
   }
 
   def getInverseIndex(graph: Graph, nodeKind: Int, propertyKind: Int): MultiDictIndex[GNode] = {

core/src/main/scala/flatgraph/misc/TestUtils.scala

@@ -60,7 +60,24 @@ object TestUtils {
 
       newGraph
     }
+  }
+
+  /** copies a single GNode into a different graph, including all properties, but excluding edges */
+  def copyNode(node: GNode, targetGraph: Graph): GNode = {
+    assert(node.graph.schema == targetGraph.schema, "schemas of the two graphs must be identical, but they are not...")
+    // first pass: create raw node
+    val newNode = new GenericDNode(node.nodeKind)
+    DiffGraphApplier.applyDiff(targetGraph, new DiffGraphBuilder(targetGraph.schema).addNode(newNode))
+    val nodeInTargetGraph = newNode.storedRef.get // this is set by `applyDiff`
+
+    // second pass: set node properties
+    val diffGraphForProperties = new DiffGraphBuilder(targetGraph.schema)
+    for {
+      (propertyKind, value) <- Accessors._getNodeProperties(node)
+    } diffGraphForProperties._setNodeProperty(nodeInTargetGraph, propertyKind, value)
 
+    DiffGraphApplier.applyDiff(targetGraph, diffGraphForProperties)
+    nodeInTargetGraph
   }
 
 }

core/src/test/scala/flatgraph/GraphTests.scala

@@ -3,10 +3,12 @@ package flatgraph
 import flatgraph.TestHelpers.withTemporaryFile
 import flatgraph.TestSchema.testSerialization
 import flatgraph.misc.DebugDump.debugDump
+import flatgraph.misc.TestUtils
 import flatgraph.storage.Deserialization
 import flatgraph.storage.Deserialization.DeserializationException
 import flatgraph.traversal.language.*
 import flatgraph.util.DiffToolTests
+import flatgraph.util.DiffToolTests.sampleSchema
 import org.scalatest.matchers.should.Matchers
 import org.scalatest.matchers.should.Matchers.shouldBe
 import org.scalatest.wordspec.AnyWordSpec
@@ -1091,4 +1093,26 @@ class GraphTests extends AnyWordSpec with Matchers {
     // original graph should be untouched
     debugDump(graph) shouldBe debugDumpOriginalGraph
   }
+
+  "copy a single node (ignoring edges)" in {
+    val graphA = DiffToolTests.makeSampleGraph()
+    debugDump(graphA) shouldBe
+      """#Node numbers (kindId, nnodes) (0: 2), total 2
+        |Node kind 0. (eid, nEdgesOut, nEdgesIn): (0, 1 [dense], 1 [dense]),
+        |   V0_0       : 0: [A], 1: [40]
+        |   V0_0   [0] -> (edgePropertyValue) V0_1
+        |   V0_1       : 0: [X, Y], 1: [50, 51]
+        |   V0_1   [0] <- (edgePropertyValue) V0_0
+        |""".stripMargin
+
+    val V0_1   = graphA.node(kind = 0, seq = 1)
+    val graphB = new Graph(sampleSchema)
+    TestUtils.copyNode(V0_1, graphB)
+
+    debugDump(graphB) shouldBe
+      """#Node numbers (kindId, nnodes) (0: 1), total 1
+        |Node kind 0. (eid, nEdgesOut, nEdgesIn): (0, 0 [NA], 0 [NA]),
+        |   V0_0       : 0: [X, Y], 1: [50, 51]
+        |""".stripMargin
+  }
 }