# Revit Element Collector

> Query the Revit model with the Nice3point.Revit.Extensions fluent FilteredElementCollector wrappers; filter with Revit's parameter filters, not by loading elements and filtering with LINQ. USE FOR: writing or reviewing element queries that filter by class, category, or parameter value and return the first match, a count, or the full set. DO NOT USE FOR: reading or setting parameters on an element already in hand (use revit-element-and-parameter-access).

- Skill: `nice3point/revit-element-collector` (Agent Skill)
- Install (CLI): `npx skillmds@latest add nice3point/revit-element-collector`
- Raw SKILL.md: https://api.skillmd.com/api/skills/nice3point/revit-element-collector/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- License: MIT
- Author: nice3point (https://skillmd.com/u/nice3point)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/nice3point/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

```csharp
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.

```csharp
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.

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

```csharp
// 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).

```csharp
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

| Pitfall                                                                            | Correct approach                                                            |
|------------------------------------------------------------------------------------|-----------------------------------------------------------------------------|
| `.Where(element => element.get_Parameter(...).AsDouble() > x)` after the collector | `WhereParameter(param).IsGreaterThan(x, epsilon)` — a native rule.          |
| `collector.ToElements().Count` / `.Any()` (LINQ over the list)                     | `collector.Count()` / `collector.Any()` — native fast paths.                |
| Comparing `double` parameters without an epsilon                                   | Use the `IsGreaterThan(value, epsilon)` overload.                           |
| `CollectElements` or `WhereParameter` not found                                    | The `Nice3point.Revit.Extensions` package is not referenced in the project. |
| Reusing one collector after a terminator                                           | Start a fresh `CollectElements()` per query; terminators stop the iterator. |