public void TestGraphSccAlgorithm()
{
//This test uses a simple graph from the wikipedia page about SCC: http://en.wikipedia.org/wiki/Strongly_connected_components
// The copy of this image is in SccTestGraph.jpg file in this test project.
var expected = "a, Scc=1; b, Scc=1; e, Scc=1; c, Scc=2; d, Scc=2; h, Scc=2; f, Scc=3; g, Scc=3"; //expected SCC indexes
var gr = new Graph();
SetupSampleGraph(gr);
gr.BuildScc();
// additionally sort by tags, so that result string matches
var sortedVertexes = gr.Vertexes.OrderBy(v => v.SccIndex).ThenBy(v => (string)v.Tag).ToList();
var strOut = string.Join("; ", sortedVertexes);
Assert.AreEqual(expected, strOut, "SCC computation did not return expected result.");
}
// Builds a sample graph from http://en.wikipedia.org/wiki/Strongly_connected_components
private static void SetupSampleGraph(Graph gr)
{
var a = gr.Add("a");
var b = gr.Add("b");
var c = gr.Add("c");
var d = gr.Add("d");
var e = gr.Add("e");
var f = gr.Add("f");
var g = gr.Add("g");
var h = gr.Add("h");
//links
a.AddLink(b);
b.AddLink(e, f, c);
c.AddLink(d, g);
d.AddLink(c, h);
e.AddLink(a, f);
f.AddLink(g);
g.AddLink(f);
h.AddLink(g, d);
}
//Sequences set of records in a looped non-trivial entity group. Assigns record.SortSubIndex value after sequencing
private void SequenceSubGroup(IEnumerable<EntityRecord> records)
{
var graph = new Graph();
foreach (var rec in records) {
var ent = rec.EntityInfo;
foreach (var refMember in ent.RefMembers) {
var targetEnt = rec.GetValue(refMember);
//If reference is not modified or not set, then nothing to do
if (targetEnt == null)
continue;
var targetRec = EntityHelper.GetRecord(targetEnt);
// we are interested only in case when both records are inserted, or both are deleted.
if (targetRec.Status != rec.Status)
continue;
// finally, the target record's table must be in the same SCC group - i.e. have the same SccIndex
if (targetRec.EntityInfo.TopologicalIndex != rec.EntityInfo.TopologicalIndex)
continue;
// We have potential conflict; add vertexes and link for the conflict
var thisV = graph.FindOrAdd(rec);
var targetV = graph.FindOrAdd(targetRec);
thisV.AddLink(targetV);
}
}//foreach cmd
//Check if any conflicts found
if (graph.Vertexes.Count == 0) return;
//Build SCC graph
graph.BuildScc();
// Once SCC is built, we have SCC indexes in Vertexes; use them to assign Record's TopologicalIndex
bool hasNonTrivialGroups = false;
foreach (var v in graph.Vertexes) {
var rec = (EntityRecord)v.Tag;
rec.SortSubIndex = rec.Status == EntityStatus.New ? -v.SccIndex : v.SccIndex;
hasNonTrivialGroups |= v.NonTrivialGroup;
}
//if there are non-trivial groups, it means we have circular references in the set.
if (hasNonTrivialGroups) {
var entList = string.Join(",", records.Select(r=> r.PrimaryKey.ToString()));
var msg = StringHelper.SafeFormat("Detected circular references between entities in an update set. Cannot commit group update. Entities: [{0}].", entList);
var fault = new ClientFault() {Code = ClientFaultCodes.CircularEntityReference, Message = msg};
var faultEx = new ClientFaultException(new[] { fault });
faultEx.LogAsError = true;
throw faultEx;
}
}