/// <inheritdoc/>
public override bool TryHandleEnter(
Neo4JProjectionVisitorContext context,
ISelection selection,
[NotNullWhen(true)] out ISelectionVisitorAction?action)
{
++context.CurrentLevel;
selection.Field.ContextData.TryGetValue(
nameof(Neo4JRelationshipAttribute),
out object?relationship);
if (relationship is Neo4JRelationshipAttribute rel)
{
context.RelationshipTypes.Push(rel);
}
context.StartNodes.Push(Cypher.NamedNode(selection.DeclaringType.Name.Value));
if (context.RelationshipProjections.ContainsKey(context.CurrentLevel))
{
context.RelationshipProjections[context.CurrentLevel]
.Enqueue(selection.Field.GetName());
}
else
{
Queue <object> queue = new();
queue.Enqueue(selection.Field.GetName());
context.RelationshipProjections.Add(context.CurrentLevel, queue);
}
action = SelectionVisitor.Continue;
return(true);
}
public static bool TryCreateRelationshipProjection(
this Neo4JProjectionVisitorContext context,
[NotNullWhen(true)] out PatternComprehension?patternComprehension)
{
patternComprehension = new PatternComprehension(
context.Relationships.Peek(),
context.EndNodes.Peek()
.Project(context.RelationshipProjections[context.CurrentLevel].ToArray()));
return(true);
}
public static bool TryCreateQuery(
this Neo4JProjectionVisitorContext context,
[NotNullWhen(true)] out object[]?query)
{
query = null;
if (context.Projections.Count == 0)
{
return(false);
}
query = context.Projections.ToArray();
return(true);
}
/// <inheritdoc/>
public override bool TryHandleEnter(
Neo4JProjectionVisitorContext context,
ISelection selection,
out ISelectionVisitorAction action)
{
IObjectField field = selection.Field;
action = SelectionVisitor.SkipAndLeave;
if (!context.StartNodes.Any())
{
context.Projections.Add(field.GetName());
return(true);
}
if (context.StartNodes.Count != context.EndNodes.Count)
{
context.EndNodes.Push(Cypher.NamedNode(selection.DeclaringType.Name.Value));
}
if (context.StartNodes.Count != context.Relationships.Count)
{
Neo4JRelationshipAttribute rel = context.RelationshipTypes.Peek();
Node startNode = context.StartNodes.Peek();
Node endNode = context.EndNodes.Peek();
Relationship direction = rel.Direction switch
{
Incoming => startNode.RelationshipFrom(endNode, rel.Name),
Outgoing => startNode.RelationshipTo(endNode, rel.Name),
None => startNode.RelationshipBetween(endNode, rel.Name),
_ => throw new InvalidOperationException(
Neo4JResources.Projection_RelationshipDirectionNotSet)
};
context.Relationships.Push(direction);
}
context
.RelationshipProjections[context.CurrentLevel]
.Enqueue(selection.Field.GetName());
return(true);
}
}
/// <inheritdoc/>
public override FieldMiddleware CreateExecutor <TEntityType>()
{
return(next => context => ExecuteAsync(next, context));
async ValueTask ExecuteAsync(
FieldDelegate next,
IMiddlewareContext context)
{
// first we let the pipeline run and produce a result.
await next(context).ConfigureAwait(false);
if (context.Result is not null)
{
var visitorContext =
new Neo4JProjectionVisitorContext(context, context.ObjectType);
var visitor = new ProjectionVisitor <Neo4JProjectionVisitorContext>();
visitor.Visit(visitorContext);
if (!visitorContext.TryCreateQuery(out object[]? projections) ||
visitorContext.Errors.Count > 0)
{
context.Result = Array.Empty <TEntityType>();
foreach (IError error in visitorContext.Errors)
{
context.ReportError(error.WithPath(context.Path));
}
}
else
{
context.LocalContextData =
context.LocalContextData.SetItem("ProjectionDefinition", projections);
await next(context).ConfigureAwait(false);
if (context.Result is INeo4JExecutable executable)
{
context.Result = executable.WithProjection(projections);
}
}
}
}
/// <inheritdoc/>
public override bool TryHandleLeave(
Neo4JProjectionVisitorContext context,
ISelection selection,
[NotNullWhen(true)] out ISelectionVisitorAction?action)
{
if (context.StartNodes.Any())
{
object field = context.RelationshipProjections[context.CurrentLevel].Dequeue();
context.TryCreateRelationshipProjection(out PatternComprehension? projections);
switch (context.CurrentLevel)
{
case > 1:
context.RelationshipProjections[context.CurrentLevel - 1].Enqueue(field);
context.RelationshipProjections[context.CurrentLevel - 1]
.Enqueue(projections);
break;
case 1:
context.Projections.Push(field);
context.Projections.Push(projections);
break;
}
}
--context.CurrentLevel;
context.StartNodes.Pop();
context.EndNodes.Pop();
context.Relationships.Pop();
if (context.CurrentLevel == 0)
{
context.RelationshipProjections.Clear();
}
action = SelectionVisitor.Continue;
return(true);
}