Struct QueryEvaluator

pub struct QueryEvaluator { /* private fields */ }

Evaluates a query against a given RDF dataset

Note that this evaluator does not handle the FROM and FROM NAMED part of the query. You must select the proper dataset before using this struct.

To adapt this software to work on your own RDF dataset, you need to implement the QueryableDataset trait.

use oxrdf::{Dataset, GraphName, NamedNode, Quad};
use spareval::{QueryEvaluator, QueryResults};
use spargebra::Query;

let ex = NamedNode::new("http://example.com")?;
let dataset = Dataset::from_iter([Quad::new(
    ex.clone(),
    ex.clone(),
    ex.clone(),
    GraphName::DefaultGraph,
)]);
let query = Query::parse("SELECT * WHERE { ?s ?p ?o }", None)?;
let results = QueryEvaluator::new().execute(dataset, &query);
if let QueryResults::Solutions(solutions) = results? {
    let solutions = solutions.collect::<Result<Vec<_>, _>>()?;
    assert_eq!(solutions.len(), 1);
    assert_eq!(solutions[0]["s"], ex.into());
}

Implementations

impl QueryEvaluator

pub fn new() -> Self

pub fn execute( &self, dataset: impl QueryableDataset, query: &Query, ) -> Result<QueryResults, QueryEvaluationError>

pub fn execute_with_substituted_variables( &self, dataset: impl QueryableDataset, query: &Query, substitutions: impl IntoIterator<Item = (Variable, Term)>, ) -> Result<QueryResults, QueryEvaluationError>

Executes a SPARQL query while substituting some variables with the given values.

Substitution follows RDF-dev SEP-0007.

use oxrdf::{Dataset, GraphName, NamedNode, Quad, Variable};
use spareval::{QueryEvaluator, QueryResults};
use spargebra::Query;

let ex = NamedNode::new("http://example.com")?;
let dataset = Dataset::from_iter([Quad::new(
    ex.clone(),
    ex.clone(),
    ex.clone(),
    GraphName::DefaultGraph,
)]);
let query = Query::parse("SELECT * WHERE { ?s ?p ?o }", None)?;
let results = QueryEvaluator::new().execute_with_substituted_variables(
    dataset,
    &query,
    [(Variable::new("s")?, ex.clone().into())],
);
if let QueryResults::Solutions(solutions) = results? {
    let solutions = solutions.collect::<Result<Vec<_>, _>>()?;
    assert_eq!(solutions.len(), 1);
    assert_eq!(solutions[0]["s"], ex.into());
}

pub fn explain( &self, dataset: impl QueryableDataset, query: &Query, ) -> (Result<QueryResults, QueryEvaluationError>, QueryExplanation)

pub fn explain_with_substituted_variables( &self, dataset: impl QueryableDataset, query: &Query, substitutions: impl IntoIterator<Item = (Variable, Term)>, ) -> (Result<QueryResults, QueryEvaluationError>, QueryExplanation)

pub fn with_service_handler( self, service_name: impl Into<NamedNode>, handler: impl ServiceHandler + 'static, ) -> Self

Use a given ServiceHandler to execute SPARQL 1.1 Federated Query SERVICE calls.

See ServiceHandler for an example.

pub fn with_default_service_handler( self, handler: impl DefaultServiceHandler + 'static, ) -> Self

Use a given DefaultServiceHandler to execute SPARQL 1.1 Federated Query SERVICE calls if no explicit service handler is defined for the service.

See DefaultServiceHandler for an example.

pub fn has_default_service_handler(&self) -> bool

pub fn with_custom_function( self, name: NamedNode, evaluator: impl Fn(&[Term]) -> Option<Term> + Send + Sync + 'static, ) -> Self

Adds a custom SPARQL evaluation function.

Example with a function serializing terms to N-Triples:

use oxrdf::{Dataset, Literal, NamedNode};
use spareval::{QueryEvaluator, QueryResults};
use spargebra::Query;

let evaluator = QueryEvaluator::new().with_custom_function(
    NamedNode::new("http://www.w3.org/ns/formats/N-Triples")?,
    |args| args.get(0).map(|t| Literal::from(t.to_string()).into()),
);
let query = Query::parse(
    "SELECT (<http://www.w3.org/ns/formats/N-Triples>(1) AS ?nt) WHERE {}",
    None,
)?;
if let QueryResults::Solutions(mut solutions) = evaluator.execute(Dataset::new(), &query)? {
    assert_eq!(
        solutions.next().unwrap()?.get("nt"),
        Some(&Literal::from("\"1\"^^<http://www.w3.org/2001/XMLSchema#integer>").into())
    );
}

pub fn without_optimizations(self) -> Self

Disables query optimizations and runs the query as it is.

pub fn compute_statistics(self) -> Self

Compute statistics during evaluation and fills them in the explanation tree.

Trait Implementations

impl Clone for QueryEvaluator

fn clone(&self) -> QueryEvaluator

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Default for QueryEvaluator

fn default() -> QueryEvaluator

Returns the “default value” for a type.