Optimal detection of circular reference in object (currently brute forcing) - algorithm

Question

I have a Product object, which can depend on other products.
This dependency information is stored in a ServiceTemplate object.
These dependencies can be chained (i use the arrow to indicate that 3 depends on 2, and 2 depends on 1):
1 <= 2 <= 3
I need to prevent circular references, where with the above 1 could be set to depend on 3 this causing a loop.
This is hashed up from how i think it may work but is brute forcing the solution - what would be the optimal algorithm approach or is this already the best way?
class Program
{
class Product
{
public Product(int id)
{
this.id = id;
}
private readonly int id;
public int Id { get { return this.id; } }
}
class ServiceTemplate
{
// stores the list of other products that a product depends on
Dictionary<int, List<int>> relationships = new Dictionary<int, List<int>>();
public void SetRequires(Product on, Product requires)
{
if (WouldCauseCircularDepdndency(on.Id, requires.Id) == true)
throw new ArgumentException("circular dependencies not allowed");
List<int> list = null;
this.relationships.TryGetValue(on.Id, out list);
if(list==null)
{
list = new List<int>();
this.relationships.Add(on.Id, list);
}
list.Add(requires.Id);
}
private bool WouldCauseCircularDepdndency(int on, int requires)
{
// get relationships of product we will depend on
List<int> list = null;
this.relationships.TryGetValue(requires, out list);
if (list == null)
{
return false;
}
else if (list.Contains(on))
{
return true;
}
else
{
foreach (var id in list)
{
// traverse each child recursively
if (WouldCauseCircularDepdndency(on, id))
return true;
}
}
return false; // if we got this far, no circular references detected
}
}
static void Main(string[] args)
{
var windows = new Product(1);
var linux = new Product(2);
var mySql = new Product(3);
var ms_sql = new Product(4);
var cluster = new Product(5);
var other = new Product(6);
var config = new ServiceTemplate();
config.SetRequires(mySql, windows); // mySql requires windows
config.SetRequires(mySql, linux); // mySql requires linux
config.SetRequires(ms_sql, windows); // microsoft sql requires windows
config.SetRequires(cluster, ms_sql); // cluster requires microsoft sql
config.SetRequires(other, cluster);
// this should throw an exception due to circular dependency
config.SetRequires(windows, other);
/* at this point the config relationships dictionary is as follows:
3 => 1,2
4 => 1
5 => 4
5 => 6
1 => 6
*/
}
}

Answer 1

You could try topological sorting. If it can be constructed, you have no circular dependency. Otherwise, you have a cycle.

Answer 2

I ended up using the QuickGraph nuget package and an AdjacencyGraph<int,Edge<int>>, once the relationship is added i try and to a TopologicalSort() as advised by #Vesi:
class Program
{
class Product
{
public Product(int id)
{
this.id = id;
}
private readonly int id;
public int Id { get { return this.id; } }
}
class ServiceTemplate
{
// stores the list of other products that a product depends on
AdjacencyGraph<int, Edge<int>> relationshipGraph = new AdjacencyGraph<int, Edge<int>>();
public void SetRequires(Product on, Product requires)
{
var toAdd = new Edge<int>(on.Id, requires.Id);
this.relationshipGraph.AddVerticesAndEdge(toAdd);
try
{
var list = this.relationshipGraph.TopologicalSort();
}
catch (NonAcyclicGraphException)
{
this.relationshipGraph.RemoveEdge(toAdd);
throw new ArgumentException("Circular dependencies not allowed");
}
}
}
static void Main(string[] args)
{
var windows = new Product(1);
var linux = new Product(2);
var mySql = new Product(3);
var ms_sql = new Product(4);
var cluster = new Product(5);
var other = new Product(6);
var config = new ServiceTemplate();
config.SetRequires(mySql, windows); // mySql requires windows
config.SetRequires(mySql, linux); // mySql requires linux
config.SetRequires(ms_sql, windows); // microsoft sql requires windows
config.SetRequires(cluster, ms_sql); // cluster requires microsoft sql
config.SetRequires(other, cluster);
// this should throw an exception due to circular dependency
config.SetRequires(windows, other);
}
}