Revit Element Collector

Revit Element Collector

Query the model through the fluent FilteredElementCollector wrappers in Nice3point.Revit.Extensions. They wrap the raw Revit collector API into a single readable chain and keep filtering inside Revit's native database engine. The database engine evaluates the filters before elements expand into memory. Filtering the collector output with LINQ materializes every element first.

When to use

• Retrieving elements, types, or instances by class, category, or parameter value.
• Reviewing code that writes new FilteredElementCollector(document) by hand or filters collector output with .Where(...).
• Fetching the first match or a count without loading the whole result set.

When not to use

• Reading or setting parameters on an element already in hand — use revit-element-and-parameter-access.
• Applying a specialized ElementFilter the extensions do not expose — fall back to a raw FilteredElementCollector with that filter.

Workflow

Always prefer the built-in methods of FilteredElementCollector extensions over using LINQ. LINQ materializes and marshals every element into the .NET process's memory and does not filter at the database level; use it only if the built-in methods are insufficient for filtering.

Step 1: Open a collector from the document

var collector = document.CollectElements(); // whole document
var viewScoped = document.CollectElements(view); // elements visible in a view
var restricted = document.CollectElements(elementIds); // a known id set

Step 2: Apply quick filters as generic, typed calls

Prefer the generic and multi-argument overloads over raw typeof filters.

var walls = document.CollectElements()
    .OfClass<Wall>()
    .ToElements();

var openings = document.CollectElements()
    .OfCategories(BuiltInCategory.OST_Walls, BuiltInCategory.OST_Floors)
    .Instances() // only instances; use .Types() for element types
    .ToElements();

var annotated = document.CollectElements()
    .WithExtensibleStorage(schemaGuid) // elements carrying add-in data
    .ToElements();

Step 3: Filter by parameter with native rules, not LINQ

WhereParameter builds a native ElementParameterFilter — evaluated at the database level before element expansion — then continues the collector chain.

var tallWalls = document.CollectElements()
    .OfClass<Wall>()
    .WhereParameter(BuiltInParameter.WALL_USER_HEIGHT_PARAM).IsGreaterThan(3.0, 1e-6)
    .ToElements();

// BAD — loads every wall into memory, then filters
var tallWalls = new FilteredElementCollector(document)
    .OfClass(typeof(Wall))
    .Cast<Wall>()
    .Where(wall => wall.get_Parameter(BuiltInParameter.WALL_USER_HEIGHT_PARAM).AsDouble() > 3.0);

Comparisons include Equals, IsGreaterThan/IsGreaterThanOrEqualTo, IsLessThan/IsLessThanOrEqualTo (with an optional double epsilon), Contains/StartsWith (and their Not… inversions), and HasValue.

Step 4: Terminate with the fast native path

Use the extension terminators, not LINQ; they call Revit's native fast implementations (Count() uses the fast GetElementCount() implementation).

var firstRoom = document.CollectElements().OfClass<SpatialElement>().FirstOrDefault();
var wallCount = document.CollectElements().OfClass<Wall>().Count();
var hasLevels = document.CollectElements().OfClass<Level>().Any();

Step 5: Verify

1. The query builds the filter through collector methods, not .Where(...) over materialized elements.
2. A parameter comparison uses WhereParameter, not a post-collection predicate.
3. The terminator is a native call (ToElements, First, FirstOrDefault, Count, Any).

Validation

• The collector comes from document.CollectElements(...), not a hand-written new FilteredElementCollector(...).
• Class and category filters use the generic/multi-argument extensions.
• Parameter conditions use WhereParameter(...), filtering at the database level.
• Single-result and count queries use First/FirstOrDefault/Count/Any, not LINQ.
• A quick filter (class/category) precedes a slow filter (parameter) to shrink the candidate set.

Common Pitfalls