/// <summary>
/// Sorts tables by the foreign key dependencies.
/// </summary>
/// <param name="databaseSchema">The database schema.</param>
/// <returns></returns>
public static IEnumerable<DatabaseTable> TopologicalSort(DatabaseSchema databaseSchema)
{
var tables = databaseSchema.Tables;
var sorter = new TopologicalSorter(tables.Count);
var indexes = new Dictionary<string, int>();
//add vertices
for (var i = 0; i < tables.Count; i++)
{
indexes[tables[i].Name] = sorter.AddVertex(i);
}
//add edges
for (var i = 0; i < tables.Count; i++)
{
foreach (var t in tables[i].ForeignKeys)
{
//ignore cycles (not relevant here)
if (t.RefersToTable == tables[i].Name) continue;
//corrupt model
if (!indexes.ContainsKey(t.RefersToTable)) continue;
sorter.AddEdge(i, indexes[t.RefersToTable]);
}
}
try
{
var sortedIndex = sorter.Sort();
return sortedIndex.Reverse().Select(i => tables[i]);
}
catch (InvalidOperationException)
{
//Bidirectional foreign keys create a cyclic dependency
//Topological sort won't work
//There is no way to sort by insert order for two such tables
//Just give them the tables back, with those with least foreign keys at the start.
return tables.OrderBy(t => t.ForeignKeys.Count);
}
}