First Step

The first step consumes the walker and returns the ID of the very first element encountered in the traversal stream, wrapped in an Option. If the stream is empty, it returns None. This is a terminal operation that efficiently short-circuits the traversal as soon as the first element is found.

In this diagram:

• Input Elements: The walker starts with elements A, B, C, D.
• The .first() step processes the stream, immediately takes element A, and consumes the walker. Elements B, C, and D are never processed or considered.
• Returns: Option<ID>: The step returns Some(ID(A)), containing the ID of the first element found.
• Terminates Walker: This step ends the Graph API walker chain.

Syntax

walker.first()

Parameters

This step takes no parameters.

Return Value

Returns an Option containing the first element from the traversal, or None if the traversal is empty.

Examples

Basic Usage

Retrieve the first person vertex from the graph:

    // Get the first person in the graph (if any)
    let first_person = graph.walk().vertices(Vertex::person()).first();

    match first_person {
        Some(person) => println!("Found a person: {:?}", person),
        None => println!("No people in the graph"),
    }

With Filtering

Get the first person matching specific criteria:

    // Get the first person with a specific name
    let first_bryn = graph
        .walk()
        .vertices(Vertex::person()) // Get all Person vertices
        .filter_by_person(|person, _| {
            // Using the typed projection with accessor methods
            person.name().contains("Bryn")
        })
        .first();

    match first_bryn {
        Some(bryn) => println!("Found Bryn: {:?}", bryn),
        None => println!("No one named Bryn in the graph"),
    }

Existence Check

Check if any elements match a condition:

    // Use first to check if any element matches a condition
    let has_young_person = graph
        .walk()
        .vertices(Vertex::person())
        .filter_by_person(|person, _| {
            // Using type-safe accessor methods
            person.age() < 30
        })
        .first()
        .is_some();

    println!(
        "Graph {} people under 30",
        if has_young_person {
            "contains"
        } else {
            "doesn't contain"
        }
    );

Best Practices

• Always handle the None case when using first() on potentially empty traversals
• Use filtering before first() to ensure you get the element you want
• For deterministic results, combine with ordered indexes or explicit sorting
• Prefer first() over limit(1).collect::<Vec<_>>() for better performance

Common Use Cases

• Single element retrieval: Getting exactly one element matching specific criteria
• Existence checking: Determining if any elements match a condition with is_some()
• Quick lookup: Finding a representative example of a vertex or edge type
• Early termination: Efficiently stopping traversal after finding the first match