// Note about special case: members with CascadeDelete attribute.
// Demo case setup. 3 entities, IBook, IAuthor, and IBookAuthor as link table; IBookAuthor references IBook with CascadeDelete,
// and references IAuthor without cascade.
// Because of CascadeDelete, when we delete IBook and IBookAuthor in one operation, the order of IBook vs IBookAuthor does not matter:
// even if IBook comes before IBookAuthor, delete will succeed because of cascade delete of IBookAuthor.
// The problem case is when we are deleting IBook and IAuthor, without explicitly deleting IBookAuthor.
// In this case IAuthor should be deleted after IBook - otherwise still existing IBookAuthor record
// would prevent it from deleting. As there's no explicit IBookAuthor in delete set, and there's
// no FK links between IAuthor and IBook - then they may come to delete in any order, and trans might fail.
// The solution is to introduce an extra direct link between IBook and IAuthor in abstract SCC node tree.
// This extra link will ensure proper topological ordering of IBook and IAuthor.
// Note that we still need to add link between IBookAuthor and IBook - for proper ordering of inserts.
private void ComputeTopologicalIndexes()
{
// Run SCC algorithm
var g = new SccGraph();
//Perform SCC analysis.
foreach (var ent in Model.Entities)
{
ent.SccVertex = g.Add(ent);
}
//setup links
foreach (var ent in Model.Entities)
{
var cascadeMembers = new List <EntityMemberInfo>();
var nonCascadeMembers = new List <EntityMemberInfo>();
foreach (var member in ent.RefMembers)
{
var targetEnt = member.ReferenceInfo.ToKey.Entity;
ent.SccVertex.AddLink(targetEnt.SccVertex);
if (member.Flags.IsSet(EntityMemberFlags.CascadeDelete))
{
cascadeMembers.Add(member);
}
else
{
nonCascadeMembers.Add(member);
}
}//foreach member
//For all cascade member (IBookAuthor.Author) targets add direct links to all non-cascade member targets
// (from IBook to IAuthor)
foreach (var cascMember in cascadeMembers)
{
var cascTarget = cascMember.ReferenceInfo.ToKey.Entity;
foreach (var nonCascMember in nonCascadeMembers)
{
var nonCascTarget = nonCascMember.ReferenceInfo.ToKey.Entity;
cascTarget.SccVertex.AddLink(nonCascTarget.SccVertex);
}
} //foreach cascMember
} //foreach ent
//Build SCC
var sccCount = g.BuildScc();
//read scc index and clear vertex fields
foreach (var ent in Model.Entities)
{
var v = ent.SccVertex;
ent.TopologicalIndex = v.SccIndex;
if (v.NonTrivialGroup)
{
ent.Flags |= EntityFlags.TopologicalGroupNonTrivial;
}
ent.SccVertex = null;
}
}
// Builds a sample graph from http://en.wikipedia.org/wiki/Strongly_connected_components
private static void SetupSampleGraph(SccGraph 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);
}
