static void PopulateNodesToSqlMap(SparqlGraph g)
{
List <Node> terminalNodes = g.GetAllNodes(typeof(TerminalNode));
foreach (TerminalNode node in terminalNodes)
{
//try to match each node to sql expressions from mapping
string key = $"{node.Pred} {node.Obj}";
if (mapping.mappings.ContainsKey(key))
{
string sql = mapping.mappings[key][0].SQL;
nodesToSqlMap.Add(node, sql);
}
else
{
key = $"{node.Pred}";
if (mapping.mappings.ContainsKey(key))
{
string sql = mapping.mappings[key].Find(mapNode => mapNode.Object == node.Obj).SQL;
nodesToSqlMap.Add(node, sql);
}
else //there is no mapping for this node
{
throw new Exception($"No mapping for node {node.Subj} {node.Pred} {node.Obj} was provided!");
}
}
}
}
static string TranslateToSql(SparqlGraph g, Dictionary <string, List <MapNode> > map)
{
/*S = List of nodes in Q in a bottom-up topological order
* sqlM = a map from nodes to SQL expressions*/
List <Node> S = g.TopologicalSort();
foreach (Node n in S)
{
if (n is TerminalNode) //translating leaves
{
//skip (this step was done in PopulateNodesToSqlMap)
continue;
}
else
{
if (n is JoinNode)
{
Node n1 = n.Children[0];
Node n2 = n.Children[1];
nodesToSqlMap[n] = InnerJoin(nodesToSqlMap[n1], nodesToSqlMap[n2]);
}
else if (n is OptionalNode)
{
Node n1 = n.Children[0];
Node n2 = n.Parent;
string e = (n as OptionalNode).JoinCondition;
nodesToSqlMap[n] = LeftJoin(nodesToSqlMap[n1], nodesToSqlMap[n2], e);
}
else if (n is UnionNode)
{
Node n1 = n.Children[0];
Node n2 = n.Children[1];
nodesToSqlMap[n] = Union(nodesToSqlMap[n1], nodesToSqlMap[n2]);
}
else if (n is FilterNode)
{
Node n1 = n.Children[0];
string e = (n as FilterNode).FilterExpression;
nodesToSqlMap[n] = Filter(nodesToSqlMap[n1], e);
}
else if (n is ProjectNode)
{
Node n1 = n.Children[0];
List <string> pv = (n as ProjectNode).ProjectionVariables;
nodesToSqlMap[n] = Project(nodesToSqlMap[n1], pv);
}
}
}
return(nodesToSqlMap[S.Last()]);
}