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use std::{collections::BTreeMap, fmt::Debug, sync::Arc};
use itertools::Itertools;
use serde::{de::DeserializeOwned, Deserialize, Serialize};
use crate::{
ir::{EdgeParameters, Eid, FieldRef, FieldValue, IndexedQuery, Type, Vid},
util::BTreeMapTryInsertExt,
};
use self::error::QueryArgumentsError;
pub mod basic_adapter;
pub mod error;
pub mod execution;
mod filtering;
pub mod helpers;
mod hints;
pub mod replay;
pub mod trace;
pub use hints::{
CandidateValue, DynamicallyResolvedValue, EdgeInfo, NeighborInfo, QueryInfo, Range,
RequiredProperty, ResolveEdgeInfo, ResolveInfo, VertexInfo,
};
/// An iterator of vertices representing data points we are querying.
pub type VertexIterator<'vertex, VertexT> = Box<dyn Iterator<Item = VertexT> + 'vertex>;
/// An iterator of query contexts: bookkeeping structs we use to build up the query results.
///
/// Each context represents a possible result of the query. At each query processing step,
/// all the contexts at that step have fulfilled all the query conditions thus far.
///
/// This type is usually an input to adapter resolver functions. Calling those functions
/// asks them to resolve a property, edge, or type coercion for the particular vertex
/// the context is currently processing at that point in the query.
pub type ContextIterator<'vertex, VertexT> = VertexIterator<'vertex, DataContext<VertexT>>;
/// Iterator of (context, outcome) tuples: the output type of most resolver functions.
///
/// Resolver functions produce an output value for each context:
/// - resolve_property() produces that property's value;
/// - resolve_neighbors() produces an iterator of neighboring vertices along an edge;
/// - resolve_coercion() gives a bool representing whether the vertex is of the desired type.
///
/// This type lets us write those output types in a slightly more readable way.
pub type ContextOutcomeIterator<'vertex, VertexT, OutcomeT> =
Box<dyn Iterator<Item = (DataContext<VertexT>, OutcomeT)> + 'vertex>;
/// Accessor method for the `__typename` special property of Trustfall vertices.
pub trait Typename {
/// Returns the type name of this vertex in the Trustfall query graph.
///
/// Corresponds to the `__typename` special property of Trustfall vertices.
fn typename(&self) -> &'static str;
}
/// A tagged value captured and imported from another query component.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub(crate) enum TaggedValue {
/// This tagged value comes from an @optional scope that didn't exist.
/// All comparisons against it should succeed, per our spec.
NonexistentOptional,
/// This tagged value was resolved to the specified value.
Some(FieldValue),
}
/// A partial result of a Trustfall query within the interpreter defined in this module.
#[derive(Debug, Clone)]
pub struct DataContext<Vertex> {
active_vertex: Option<Vertex>,
vertices: BTreeMap<Vid, Option<Vertex>>,
values: Vec<FieldValue>,
suspended_vertices: Vec<Option<Vertex>>,
folded_contexts: BTreeMap<Eid, Option<Vec<DataContext<Vertex>>>>,
folded_values: BTreeMap<(Eid, Arc<str>), Option<ValueOrVec>>,
piggyback: Option<Vec<DataContext<Vertex>>>,
imported_tags: BTreeMap<FieldRef, TaggedValue>,
}
impl<Vertex> DataContext<Vertex> {
/// The vertex currently being processed.
///
/// For contexts passed to an [`Adapter`] resolver method,
/// this is the vertex whose data needs to be resolved.
///
/// The active vertex may be `None` when processing an `@optional` part
/// of a Trustfall query whose data did not exist. In that case:
/// - [`Adapter::resolve_property`] must produce [`FieldValue::Null`] for that context.
/// - [`Adapter::resolve_neighbors`] must produce an empty iterator of neighbors
/// such as `Box::new(std::iter::empty())` for that context.
/// - [`Adapter::resolve_coercion`] must produce a `false` coercion outcome for that context.
pub fn active_vertex<V>(&self) -> Option<&V>
where
Vertex: AsVertex<V>,
{
self.active_vertex.as_ref().and_then(AsVertex::as_vertex)
}
/// Converts `DataContext<Vertex>` to `DataContext<Other>` by mapping each `Vertex` to `Other`.
///
/// If you are implementing an [`Adapter`] for a data source,
/// you almost certainly *should not* be using this function.
/// You're probably looking for [`DataContext::active_vertex()`] instead.
pub fn map<Other>(self, mapper: &mut impl FnMut(Vertex) -> Other) -> DataContext<Other> {
DataContext {
active_vertex: self.active_vertex.map(&mut *mapper),
vertices: self.vertices.into_iter().map(|(k, v)| (k, v.map(&mut *mapper))).collect(),
values: self.values,
suspended_vertices: self
.suspended_vertices
.into_iter()
.map(|v| v.map(&mut *mapper))
.collect(),
folded_contexts: self
.folded_contexts
.into_iter()
.map(|(k, ctxs)| {
(k, ctxs.map(|v| v.into_iter().map(|ctx| ctx.map(&mut *mapper)).collect()))
})
.collect(),
folded_values: self.folded_values,
piggyback: self
.piggyback
.map(|v| v.into_iter().map(|ctx| ctx.map(&mut *mapper)).collect()),
imported_tags: self.imported_tags,
}
}
/// Map each `Vertex` to `Option<Other>`, thus converting `Self` to `DataContext<Other>`.
///
/// This is the [`DataContext`] equivalent of [`Option::and_then`][option], which is also
/// referred to as "flat-map" in some languages.
///
/// If you are implementing an [`Adapter`] for a data source,
/// you almost certainly *should not* be using this function.
/// You're probably looking for [`DataContext::active_vertex()`] instead.
///
/// [option]: https://doc.rust-lang.org/std/option/enum.Option.html#method.and_then
pub fn flat_map<T>(self, mapper: &mut impl FnMut(Vertex) -> Option<T>) -> DataContext<T> {
DataContext {
active_vertex: self.active_vertex.and_then(&mut *mapper),
vertices: self
.vertices
.into_iter()
.map(|(k, v)| (k, v.and_then(&mut *mapper)))
.collect::<BTreeMap<Vid, Option<T>>>(),
values: self.values,
suspended_vertices: self
.suspended_vertices
.into_iter()
.map(|v| v.and_then(&mut *mapper))
.collect(),
folded_contexts: self
.folded_contexts
.into_iter()
.map(|(k, ctxs)| {
(k, ctxs.map(|v| v.into_iter().map(|ctx| ctx.flat_map(&mut *mapper)).collect()))
})
.collect(),
folded_values: self.folded_values,
piggyback: self
.piggyback
.map(|v| v.into_iter().map(|ctx| ctx.flat_map(&mut *mapper)).collect()),
imported_tags: self.imported_tags,
}
}
}
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
enum ValueOrVec {
Value(FieldValue),
Vec(Vec<ValueOrVec>),
}
impl ValueOrVec {
fn as_mut_vec(&mut self) -> Option<&mut Vec<ValueOrVec>> {
match self {
ValueOrVec::Value(_) => None,
ValueOrVec::Vec(v) => Some(v),
}
}
}
impl From<ValueOrVec> for FieldValue {
fn from(v: ValueOrVec) -> Self {
match v {
ValueOrVec::Value(value) => value,
ValueOrVec::Vec(v) => v.into(),
}
}
}
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(bound = "Vertex: Debug + Clone + Serialize + DeserializeOwned")]
struct SerializableContext<Vertex> {
active_vertex: Option<Vertex>,
vertices: BTreeMap<Vid, Option<Vertex>>,
#[serde(default, skip_serializing_if = "Vec::is_empty")]
values: Vec<FieldValue>,
#[serde(default, skip_serializing_if = "Vec::is_empty")]
suspended_vertices: Vec<Option<Vertex>>,
#[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
folded_contexts: BTreeMap<Eid, Option<Vec<DataContext<Vertex>>>>,
#[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
folded_values: BTreeMap<(Eid, Arc<str>), Option<ValueOrVec>>,
#[serde(default, skip_serializing_if = "Option::is_none")]
piggyback: Option<Vec<DataContext<Vertex>>>,
/// Tagged values imported from an ancestor component of the one currently being evaluated.
#[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
imported_tags: BTreeMap<FieldRef, TaggedValue>,
}
impl<Vertex> From<SerializableContext<Vertex>> for DataContext<Vertex> {
fn from(context: SerializableContext<Vertex>) -> Self {
Self {
active_vertex: context.active_vertex,
vertices: context.vertices,
values: context.values,
suspended_vertices: context.suspended_vertices,
folded_contexts: context.folded_contexts,
folded_values: context.folded_values,
piggyback: context.piggyback,
imported_tags: context.imported_tags,
}
}
}
impl<Vertex> From<DataContext<Vertex>> for SerializableContext<Vertex> {
fn from(context: DataContext<Vertex>) -> Self {
Self {
active_vertex: context.active_vertex,
vertices: context.vertices,
values: context.values,
suspended_vertices: context.suspended_vertices,
folded_contexts: context.folded_contexts,
folded_values: context.folded_values,
piggyback: context.piggyback,
imported_tags: context.imported_tags,
}
}
}
impl<Vertex: Clone + Debug> DataContext<Vertex> {
pub fn new(vertex: Option<Vertex>) -> DataContext<Vertex> {
DataContext {
active_vertex: vertex,
piggyback: None,
vertices: Default::default(),
values: Default::default(),
suspended_vertices: Default::default(),
folded_contexts: Default::default(),
folded_values: Default::default(),
imported_tags: Default::default(),
}
}
fn record_vertex(&mut self, vid: Vid) {
self.vertices.insert_or_error(vid, self.active_vertex.clone()).unwrap();
}
fn activate_vertex(self, vid: &Vid) -> DataContext<Vertex> {
DataContext {
active_vertex: self.vertices[vid].clone(),
vertices: self.vertices,
values: self.values,
suspended_vertices: self.suspended_vertices,
folded_contexts: self.folded_contexts,
folded_values: self.folded_values,
piggyback: self.piggyback,
imported_tags: self.imported_tags,
}
}
fn split_and_move_to_vertex(&self, new_vertex: Option<Vertex>) -> DataContext<Vertex> {
DataContext {
active_vertex: new_vertex,
vertices: self.vertices.clone(),
values: self.values.clone(),
suspended_vertices: self.suspended_vertices.clone(),
folded_contexts: self.folded_contexts.clone(),
folded_values: self.folded_values.clone(),
piggyback: None,
imported_tags: self.imported_tags.clone(),
}
}
fn move_to_vertex(self, new_vertex: Option<Vertex>) -> DataContext<Vertex> {
DataContext {
active_vertex: new_vertex,
vertices: self.vertices,
values: self.values,
suspended_vertices: self.suspended_vertices,
folded_contexts: self.folded_contexts,
folded_values: self.folded_values,
piggyback: self.piggyback,
imported_tags: self.imported_tags,
}
}
fn ensure_suspended(mut self) -> DataContext<Vertex> {
if let Some(vertex) = self.active_vertex {
self.suspended_vertices.push(Some(vertex));
DataContext {
active_vertex: None,
vertices: self.vertices,
values: self.values,
suspended_vertices: self.suspended_vertices,
folded_contexts: self.folded_contexts,
folded_values: self.folded_values,
piggyback: self.piggyback,
imported_tags: self.imported_tags,
}
} else {
self
}
}
fn ensure_unsuspended(mut self) -> DataContext<Vertex> {
match self.active_vertex {
None => {
let active_vertex = self.suspended_vertices.pop().unwrap();
DataContext {
active_vertex,
vertices: self.vertices,
values: self.values,
suspended_vertices: self.suspended_vertices,
folded_contexts: self.folded_contexts,
folded_values: self.folded_values,
piggyback: self.piggyback,
imported_tags: self.imported_tags,
}
}
Some(_) => self,
}
}
}
impl<Vertex: PartialEq> PartialEq for DataContext<Vertex> {
fn eq(&self, other: &Self) -> bool {
self.active_vertex == other.active_vertex
&& self.vertices == other.vertices
&& self.values == other.values
&& self.suspended_vertices == other.suspended_vertices
&& self.folded_contexts == other.folded_contexts
&& self.piggyback == other.piggyback
&& self.imported_tags == other.imported_tags
}
}
impl<Vertex: Eq> Eq for DataContext<Vertex> {}
impl<Vertex> Serialize for DataContext<Vertex>
where
Vertex: Debug + Clone + Serialize + DeserializeOwned,
{
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: serde::Serializer,
{
// TODO: eventually maybe write a proper (de)serialize?
SerializableContext::from(self.clone()).serialize(serializer)
}
}
impl<'de, Vertex> Deserialize<'de> for DataContext<Vertex>
where
Vertex: Debug + Clone + Serialize + DeserializeOwned,
{
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where
D: serde::Deserializer<'de>,
{
// TODO: eventually maybe write a proper (de)serialize?
SerializableContext::deserialize(deserializer).map(DataContext::from)
}
}
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct InterpretedQuery {
pub indexed_query: Arc<IndexedQuery>,
pub arguments: Arc<BTreeMap<Arc<str>, FieldValue>>,
}
impl InterpretedQuery {
#[inline]
pub fn from_query_and_arguments(
indexed_query: Arc<IndexedQuery>,
arguments: Arc<BTreeMap<Arc<str>, FieldValue>>,
) -> Result<Self, QueryArgumentsError> {
let mut errors = vec![];
let mut missing_arguments = vec![];
for (variable_name, variable_type) in &indexed_query.ir_query.variables {
match arguments.get(variable_name) {
Some(argument_value) => {
// Ensure the provided argument value is valid for the variable's inferred type.
if let Err(e) = validate_argument_type(
variable_name.as_ref(),
variable_type,
argument_value,
) {
errors.push(e);
}
}
None => {
missing_arguments.push(variable_name.as_ref());
}
}
}
if !missing_arguments.is_empty() {
errors.push(QueryArgumentsError::MissingArguments(
missing_arguments.into_iter().map(|x| x.to_string()).collect(),
));
}
let unused_arguments = arguments
.keys()
.map(|x| x.as_ref())
.filter(|arg| !indexed_query.ir_query.variables.contains_key(*arg))
.collect_vec();
if !unused_arguments.is_empty() {
errors.push(QueryArgumentsError::UnusedArguments(
unused_arguments.into_iter().map(|x| x.to_string()).collect(),
));
}
if errors.is_empty() {
Ok(Self { indexed_query, arguments })
} else {
Err(errors.into())
}
}
}
fn validate_argument_type(
variable_name: &str,
variable_type: &Type,
argument_value: &FieldValue,
) -> Result<(), QueryArgumentsError> {
if variable_type.is_valid_value(argument_value) {
Ok(())
} else {
Err(QueryArgumentsError::ArgumentTypeError(
variable_name.to_string(),
variable_type.to_string(),
argument_value.to_owned(),
))
}
}
/// Trustfall data providers implement this trait to enable querying their data sets.
///
/// The most straightforward way to implement this trait is to use
/// the [`trustfall_stubgen` code-generator tool][stubgen] tool to auto-generate stubs
/// customized to match your dataset's schema, then fill in the blanks denoted by `todo!()`.
///
/// If you prefer to implement the trait without code generation, consider implementing
/// [`BasicAdapter`](self::basic_adapter::BasicAdapter) instead. That's a simpler version
/// of this trait and can be faster to implement without a significant loss of functionality:
/// - Both traits support the same set of queries. Under the hood,
/// [`BasicAdapter`](self::basic_adapter::BasicAdapter) itself implements [`Adapter`].
/// - If you need optimizations like batching or caching, you can implement them within
/// [`BasicAdapter`](self::basic_adapter::BasicAdapter) as well.
/// - If you need more advanced optimizations such as predicate pushdown, or need to access
/// Trustfall's static analysis capabilities, implement this trait directly instead.
///
/// [stubgen]: https://docs.rs/trustfall_stubgen/latest/trustfall_stubgen/
pub trait Adapter<'vertex> {
/// The type of vertices in the dataset this adapter queries.
/// Unless your intended vertex type is cheap to clone, consider wrapping it an [`Rc`][rc]
/// or [`Arc`] to make cloning it cheaper since that's a fairly common operation
/// when queries are evaluated.
///
/// [rc]: std::rc::Rc
type Vertex: Clone + Debug + 'vertex;
/// Produce an iterator of vertices for the specified starting edge.
///
/// Starting edges are the entry points for querying according to a schema.
/// Each query starts at such an edge, and such starting edges are defined
/// directly on the root query type of the schema.
///
/// # Example
///
/// Consider this query which gets the URLs of the posts
/// currently on the front page of HackerNews: [playground][playground]
/// ```graphql
/// query {
/// FrontPage {
/// url @output
/// }
/// }
/// ```
///
/// The [HackerNews schema][schema] defines `FrontPage` as a starting edge
/// that points to vertices of type `Item`.
///
/// As part of executing this query, Trustfall will call this method
/// with `edge_name = "FrontPage"`. Here's the [implementation of this method][method]
/// in the HackerNews example adapter.
///
/// # Preconditions and postconditions
///
/// The caller guarantees that:
/// - The specified edge is a starting edge in the schema being queried.
/// - Any parameters the edge requires per the schema have values provided.
///
/// [playground]: https://play.predr.ag/hackernews#?f=2&q=*3-Get-the-HackerNews-item-URLs-of-the-items*l*3-currently-on-the-front-page.*lquery---0FrontPage---2url-*o*l--_0*J*l*J&v=--0*l*J
/// [schema]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L35
/// [method]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/adapter.rs#L128-L134
fn resolve_starting_vertices(
&self,
edge_name: &Arc<str>,
parameters: &EdgeParameters,
resolve_info: &ResolveInfo,
) -> VertexIterator<'vertex, Self::Vertex>;
/// Resolve a property required by the query that's being evaluated.
///
/// Each [`DataContext`] in the `contexts` parameter has an active vertex
/// [`DataContext::active_vertex()`]. This call is asking for the value of
/// the specified property on each such active vertex,
/// for each active vertex in the input iterator.
///
/// The most ergonomic way to implement this method is usually via
/// the [`resolve_property_with()`][resolve-property] helper method together with
/// the [`field_property!()`][field-property] and [`accessor_property!()`][accessor-property]
/// macros.
///
/// # Example
///
/// Consider this query which gets the URLs of the posts
/// currently on the front page of HackerNews: [playground][playground]
/// ```graphql
/// query {
/// FrontPage {
/// url @output
/// }
/// }
/// ```
///
/// Our HackerNews schema [defines][starting-edge] `FrontPage` as a starting edge
/// that points to vertices of type `Item`, and [defines][property] `url`
/// as a property on the `Item` type.
///
/// As part of executing this query, Trustfall will call this method
/// with `type_name = "Item"` and `property_name = "url"`.
/// This is how Trustfall looks up the URLs of the items returned by this query.
/// Here's the [implementation of this method][method] in the HackerNews example adapter.
///
/// # Preconditions and postconditions
///
/// The active vertex may be `None`, or a `Some(v)` whose `v` is of Rust type `&Self::Vertex`
/// and represents a vertex whose type in the Trustfall schema is given by
/// this function's `type_name` parameter.
///
/// The caller guarantees that:
/// - `type_name` is a type or interface defined in the schema.
/// - `property_name` is either a property field on `type_name` defined in the schema,
/// or the special value `"__typename"` requesting the name of the vertex's type.
/// - When the active vertex is `Some(...)`, its represents a vertex of type `type_name`:
/// either its type is exactly `type_name`, or `type_name` is an interface implemented by
/// the vertex's type.
///
/// The returned iterator must satisfy these properties:
/// - Produce `(context, property_value)` tuples with the property's value for that context.
/// - Produce contexts in the same order as the input `contexts` iterator produced them.
/// - Produce property values whose type matches the property's type defined in the schema.
/// - When a context's active vertex is `None`, its property value is [`FieldValue::Null`].
///
/// [playground]: https://play.predr.ag/hackernews#?f=2&q=*3-Get-the-HackerNews-item-URLs-of-the-items*l*3-currently-on-the-front-page.*lquery---0FrontPage---2url-*o*l--_0*J*l*J&v=--0*l*J
/// [starting-edge]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L35
/// [property]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L44
/// [method]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/adapter.rs#L151
/// [resolve-property]: helpers::resolve_property_with
/// [field-property]: crate::field_property
/// [accessor-property]: crate::accessor_property
fn resolve_property<V: AsVertex<Self::Vertex> + 'vertex>(
&self,
contexts: ContextIterator<'vertex, V>,
type_name: &Arc<str>,
property_name: &Arc<str>,
resolve_info: &ResolveInfo,
) -> ContextOutcomeIterator<'vertex, V, FieldValue>;
/// Resolve the neighboring vertices across an edge.
///
/// Each [`DataContext`] in the `contexts` parameter has an active vertex
/// [`DataContext::active_vertex()`]. This call is asking for
/// the iterator of neighboring vertices of the active vertex along a specified edge,
/// for each active vertex in the input iterator.
///
/// The most ergonomic way to implement this method is usually via
/// the [`resolve_neighbors_with()`][resolve-neighbors] helper method.
///
/// # Example
///
/// Consider this query which gets the usernames and karma points of the users
/// who submitted the latest stories on HackerNews: [playground][playground]
/// ```graphql
/// query {
/// Latest {
/// byUser {
/// id @output
/// karma @output
/// }
/// }
/// }
/// ```
///
/// Our HackerNews schema [defines][starting-edge] `Latest` as a starting edge
/// that points to vertices of type `Story`.
/// In turn, `Story` [has an edge][edge] called `byUser` that points to `User` vertices.
///
/// As part of executing this query, Trustfall will call this method
/// with `type_name = "Story"` and `edge_name = "byUser"`.
/// This is how Trustfall looks up the user vertices representing the submitters
/// of the latest HackerNews stories.
/// Here's the [implementation of this method][method] in the HackerNews example adapter.
///
/// # Preconditions and postconditions
///
/// The active vertex may be `None`, or a `Some(v)` whose `v` is of Rust type `&Self::Vertex`
/// and represents a vertex whose type in the Trustfall schema is given by
/// this function's `type_name` parameter.
///
/// If the schema this adapter covers has no edges aside from starting edges,
/// then this method will never be called and may be implemented as `unreachable!()`.
///
/// The caller guarantees that:
/// - `type_name` is a type or interface defined in the schema.
/// - `edge_name` is an edge field on `type_name` defined in the schema.
/// - Each parameter required by the edge has a value of appropriate type, per the schema.
/// - When the active vertex is `Some(...)`, its represents a vertex of type `type_name`:
/// either its type is exactly `type_name`, or `type_name` is an interface implemented by
/// the vertex's type.
///
/// The returned iterator must satisfy these properties:
/// - Produce `(context, neighbors)` tuples with an iterator of neighbor vertices for that edge.
/// - Produce contexts in the same order as the input `contexts` iterator produced them.
/// - Each neighboring vertex is of the type specified for that edge in the schema.
/// - When a context's active vertex is None, it has an empty neighbors iterator.
///
/// [playground]: https://play.predr.ag/hackernews#?f=2&q=*3-Get-the-usernames-and-karma-points-of-the-folks*l*3-who-submitted-the-latest-stories-on-HackerNews.*lquery---0Latest---2byUser---4id-*o*l--_4karma-*o*l--_2--*0*J*l*J&v=--0*l*J
/// [starting-edge]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L37
/// [edge]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L73
/// [method]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/adapter.rs#L225
/// [resolve-neighbors]: helpers::resolve_neighbors_with
fn resolve_neighbors<V: AsVertex<Self::Vertex> + 'vertex>(
&self,
contexts: ContextIterator<'vertex, V>,
type_name: &Arc<str>,
edge_name: &Arc<str>,
parameters: &EdgeParameters,
resolve_info: &ResolveEdgeInfo,
) -> ContextOutcomeIterator<'vertex, V, VertexIterator<'vertex, Self::Vertex>>;
/// Attempt to coerce vertices to a subtype, as required by the query that's being evaluated.
///
/// Each [`DataContext`] in the `contexts` parameter has an active vertex
/// [`DataContext::active_vertex()`]. This call is asking whether the active vertex
/// happens to be an instance of a subtype, for each active vertex in the input iterator.
///
/// The most ergonomic ways to implement this method usually rely on
/// the [`resolve_coercion_using_schema()`][resolve-schema]
/// or [`resolve_coercion_with()`][resolve-basic] helper methods.
///
/// # Example
///
/// Consider this query which gets the titles of all stories on the front page of HackerNews,
/// while discarding non-story items such as job postings and polls: [playground][playground]
/// ```graphql
/// query {
/// FrontPage {
/// ... on Story {
/// title @output
/// }
/// }
/// }
/// ```
///
/// Our HackerNews schema [defines][starting-edge] `FrontPage` as a starting edge
/// that points to vertices of type `Item`.
/// It also defines `Story` as [a subtype][subtype] of `Item`.
///
/// After resolving the `FrontPage` starting edge, Trustfall will need to determine which
/// of the resulting `Item` vertices are actually of type `Story`.
/// This is when Trustfall will call this method
/// with `type_name = "Item"` and `coerce_to_type = "Story"`.
/// Here's the [implementation of this method][method] in the HackerNews example adapter.
///
/// # Preconditions and postconditions
///
/// The active vertex may be `None`, or a `Some(v)` whose `v` is of Rust type `&Self::Vertex`
/// and represents a vertex whose type in the Trustfall schema is given by
/// this function's `type_name` parameter.
///
/// If this adapter's schema contains no subtyping, then no type coercions are possible:
/// this method will never be called and may be implemented as `unreachable!()`.
///
/// The caller guarantees that:
/// - `type_name` is an interface defined in the schema.
/// - `coerce_to_type` is a type or interface that implements `type_name` in the schema.
/// - When the active vertex is `Some(...)`, its represents a vertex of type `type_name`:
/// either its type is exactly `type_name`, or `type_name` is an interface implemented by
/// the vertex's type.
///
/// The returned iterator must satisfy these properties:
/// - Produce `(context, can_coerce)` tuples showing if the coercion succeded for that context.
/// - Produce contexts in the same order as the input `contexts` iterator produced them.
/// - Each neighboring vertex is of the type specified for that edge in the schema.
/// - When a context's active vertex is `None`, its coercion outcome is `false`.
///
/// [playground]: https://play.predr.ag/hackernews#?f=2&q=*3-Get-the-title-of-stories-on-the-HN-front-page.*l*3-Discards-any-non*-story-items-on-the-front-page*L*l*3-such-as-job-postings-or-polls.*lquery---0FrontPage---2*E-Story---4title-*o*l--_2--*0*J*l*J&v=--0*l*J
/// [starting-edge]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L35
/// [subtype]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/hackernews.graphql#L58
/// [method]: https://github.com/obi1kenobi/trustfall/blob/722f5fa6263a85ba0f376b2a5942d5a6ec17926d/trustfall/examples/hackernews/adapter.rs#L377
/// [resolve-schema]: helpers::resolve_coercion_using_schema
/// [resolve-basic]: helpers::resolve_coercion_with
fn resolve_coercion<V: AsVertex<Self::Vertex> + 'vertex>(
&self,
contexts: ContextIterator<'vertex, V>,
type_name: &Arc<str>,
coerce_to_type: &Arc<str>,
resolve_info: &ResolveInfo,
) -> ContextOutcomeIterator<'vertex, V, bool>;
}
/// Attempt to dereference a value to a `&V`, returning `None` if the value did not contain a `V`.
///
/// This trait allows types that may contain a `V` to be projected down to a `Option<&V>`.
/// It's similar in spirit to the built-in [`Deref`][deref] trait.
/// The primary difference is that [`AsVertex`] does not guarantee it'll be able to produce a `&V`,
/// instead returning `Option<&V>`. The same type may implement [`AsVertex<V>`] multiple times
/// with different `V` types, also unlike [`Deref`][deref].
///
/// [deref]: https://doc.rust-lang.org/std/ops/trait.Deref.html
pub trait AsVertex<V>: Debug + Clone {
/// Dereference this value into a `&V`, if the value happens to contain a `V`.
///
/// If this method returns `Some(&v)`, [`AsVertex::into_vertex()`] for the same `V`
/// is guaranteed to return `Some(v)` as well.
fn as_vertex(&self) -> Option<&V>;
/// Consume `self` and produce the contained `V`, if one was indeed present.
///
/// If this method returned `Some(v)`, prior [`AsVertex::as_vertex()`] calls for the same `V`
/// are guaranteed to have returned `Some(&v)` as well.
fn into_vertex(self) -> Option<V>;
}
/// Allow bidirectional conversions between a type `V` and the type implementing this trait.
///
/// Values of type `V` may be converted into the type implementing this trait, and values
/// of the implementing type may be converted into `V` via the `AsVertex<V>` supertrait.
pub trait Cast<V>: AsVertex<V> {
/// Convert a `V` into the type implementing this trait.
///
/// This is the inverse of [`AsVertex::into_vertex()`]: this function converts `vertex: V`
/// into `Self` whereas [`AsVertex::into_vertex()`] can convert the resulting `Self`
/// back into `Some(v)`.
fn into_self(vertex: V) -> Self;
}
/// Trivially, every `Debug + Clone` type is [`AsVertex`] of itself.
impl<V: Debug + Clone> AsVertex<V> for V {
fn as_vertex(&self) -> Option<&V> {
Some(self)
}
fn into_vertex(self) -> Option<V> {
Some(self)
}
}