private IEnumerable <TagConnection> GetRelatedEdgesToRemove(TagConnection edge)
{
var purgeList = new List <TagConnection>();
// 1. Rows originally inserted with the 1st AddEdge call, for this direct edge.
purgeList.AddRange(_context.TagConnections
.Where(tc => tc.DirectEdgeId == edge.Id));
// 2. All dependent rows inserted afterwards.
while (true)
{
var edgesToRemove = _context.TagConnections
.Where(tc => tc.Hops > 0)
.AsEnumerable()
.Where(tc =>
purgeList.Any(x => x.Id == tc.EntryEdgeId || x.Id == tc.ExitEdgeId) &&
purgeList.All(x => x.Id != tc.Id))
.ToList();
purgeList.AddRange(edgesToRemove);
if (!edgesToRemove.Any())
{
break;
}
}
return(purgeList);
}
private void ConnectTags(Tag child, Tag parent)
{
// 1. Direct edge.
var newDirectEdge = new TagConnection
{
SuccessorId = child.Id,
AncestorId = parent.Id,
Hops = 0
};
_context.TagConnections.Add(newDirectEdge);
_context.SaveChanges();
var newDirectEdgeId = newDirectEdge.Id;
newDirectEdge.EntryEdgeId = newDirectEdgeId;
newDirectEdge.ExitEdgeId = newDirectEdgeId;
newDirectEdge.DirectEdgeId = newDirectEdgeId;
// 2. A's incoming edges to B.
_context.TagConnections.AddRange(
_context.TagConnections
.Where(tc => tc.AncestorId == child.Id)
.Select(tc => new TagConnection
{
EntryEdgeId = tc.Id,
DirectEdgeId = newDirectEdgeId,
ExitEdgeId = newDirectEdgeId,
SuccessorId = tc.SuccessorId,
AncestorId = parent.Id,
Hops = tc.Hops + 1
})
);
// 3. A to B's outgoing edges.
_context.TagConnections.AddRange(
_context.TagConnections
.Where(tc => tc.SuccessorId == parent.Id)
.Select(tc => new TagConnection
{
EntryEdgeId = newDirectEdgeId,
DirectEdgeId = newDirectEdgeId,
ExitEdgeId = tc.Id,
SuccessorId = child.Id,
AncestorId = tc.AncestorId,
Hops = tc.Hops + 1
})
);
// 4. A's incoming edges to end vertex of B's outgoing edges.
var joinResult =
from start in _context.TagConnections
from end in _context.TagConnections
where start.AncestorId == child.Id &&
end.SuccessorId == parent.Id
select new { A = start, B = end };
_context.TagConnections.AddRange(
joinResult.Select(x => new TagConnection
{
EntryEdgeId = x.A.Id,
DirectEdgeId = newDirectEdgeId,
ExitEdgeId = x.B.Id,
SuccessorId = x.A.SuccessorId,
AncestorId = x.B.AncestorId,
Hops = x.A.Hops + x.B.Hops + 1
})
);
}
private void DeleteEdge(TagConnection edge)
{
var purgeList = GetRelatedEdgesToRemove(edge);
_context.TagConnections.RemoveRange(purgeList);
}
