apollo_federation/query_plan/

mod.rs

use std::sync::Arc;

use apollo_compiler::ExecutableDocument;
use apollo_compiler::Name;
use apollo_compiler::executable;
use serde::Deserialize;
use serde::Serialize;

use crate::query_plan::query_planner::QueryPlanningStatistics;

pub(crate) mod conditions;
pub(crate) mod display;
pub(crate) mod fetch_dependency_graph;
pub(crate) mod fetch_dependency_graph_processor;
pub mod generate;
pub mod query_planner;
pub(crate) mod query_planning_traversal;
pub mod requires_selection;
pub mod serializable_document;

pub type QueryPlanCost = f64;

#[derive(Debug, Default, PartialEq, Serialize, Deserialize)]
pub struct QueryPlan {
    pub node: Option<TopLevelPlanNode>,
    pub statistics: QueryPlanningStatistics,
}

#[derive(Debug, PartialEq, derive_more::From, Serialize, Deserialize)]
pub enum TopLevelPlanNode {
    Subscription(SubscriptionNode),
    #[from(FetchNode, Box<FetchNode>)]
    Fetch(Box<FetchNode>),
    Sequence(SequenceNode),
    Parallel(ParallelNode),
    Flatten(FlattenNode),
    Defer(DeferNode),
    #[from(ConditionNode, Box<ConditionNode>)]
    Condition(Box<ConditionNode>),
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct SubscriptionNode {
    pub primary: Box<FetchNode>,
    // XXX(@goto-bus-stop) Is this not just always a SequenceNode?
    pub rest: Option<Box<PlanNode>>,
}

#[derive(Debug, Clone, PartialEq, derive_more::From, Serialize, Deserialize)]
pub enum PlanNode {
    #[from(FetchNode, Box<FetchNode>)]
    Fetch(Box<FetchNode>),
    Sequence(SequenceNode),
    Parallel(ParallelNode),
    Flatten(FlattenNode),
    Defer(DeferNode),
    #[from(ConditionNode, Box<ConditionNode>)]
    Condition(Box<ConditionNode>),
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FetchNode {
    pub subgraph_name: Arc<str>,
    /// Optional identifier for the fetch for defer support. All fetches of a given plan will be
    /// guaranteed to have a unique `id`.
    pub id: Option<u64>,
    pub variable_usages: Vec<Name>,
    #[serde(skip_serializing_if = "Vec::is_empty")]
    #[serde(default)]
    pub requires: Vec<requires_selection::Selection>,
    // PORT_NOTE: We don't serialize the "operation" string in this struct, as these query plan
    // nodes are meant for direct consumption by router (without any serdes), so we leave the
    // question of whether it needs to be serialized to router.
    pub operation_document: serializable_document::SerializableDocument,
    pub operation_name: Option<Name>,
    #[serde(with = "crate::utils::serde_bridge::operation_type")]
    pub operation_kind: executable::OperationType,
    /// Optionally describe a number of "rewrites" that query plan executors should apply to the
    /// data that is sent as the input of this fetch. Note that such rewrites should only impact the
    /// inputs of the fetch they are applied to (meaning that, as those inputs are collected from
    /// the current in-memory result, the rewrite should _not_ impact said in-memory results, only
    /// what is sent in the fetch).
    pub input_rewrites: Arc<Vec<Arc<FetchDataRewrite>>>,
    /// Similar to `input_rewrites`, but for optional "rewrites" to apply to the data that is
    /// received from a fetch (and before it is applied to the current in-memory results).
    pub output_rewrites: Vec<Arc<FetchDataRewrite>>,
    /// Similar to the other kinds of rewrites. This is a mechanism to convert a contextual path into
    /// an argument to a resolver. Note value setters are currently unused here, but may be used in
    /// the future.
    pub context_rewrites: Vec<Arc<FetchDataRewrite>>,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct SequenceNode {
    pub nodes: Vec<PlanNode>,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ParallelNode {
    pub nodes: Vec<PlanNode>,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FlattenNode {
    pub path: Vec<FetchDataPathElement>,
    pub node: Box<PlanNode>,
}

/// A `DeferNode` corresponds to one or more `@defer` applications at the same level of "nestedness"
/// in the planned query.
///
/// It contains a "primary block" and a vector of "deferred blocks". The "primary block" represents
/// the part of the query that is _not_ deferred (so the part of the query up until we reach the
/// @defer(s) this handles), while each "deferred block" correspond to the deferred part of one of
/// the @defer(s) handled by the node.
///
/// Note that `DeferNode`s are only generated if defer support is enabled for the query planner.
/// Also note that if said support is enabled, then `DeferNode`s are always generated if the query
/// has a @defer application, even if in some cases generated plan may not "truly" defer the
/// underlying fetches (i.e. in cases where `deferred[*].node` are all undefined). This currently
/// happens because some specific cases of defer cannot be handled, but could later also happen if
/// we implement more advanced server-side heuristics to decide if deferring is judicious or not.
/// This allows the executor of the plan to consistently send a defer-abiding multipart response to
/// the client.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct DeferNode {
    /// The "primary" part of a defer, that is the non-deferred part (though could be deferred
    /// itself for a nested defer).
    pub primary: PrimaryDeferBlock,
    /// The "deferred" parts of the defer (note that it's a vector). Each of those deferred elements
    /// will correspond to a different chunk of the response to the client (after the initial
    /// on-deferred one that is).
    pub deferred: Vec<DeferredDeferBlock>,
}

/// The primary block of a `DeferNode`.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct PrimaryDeferBlock {
    /// The part of the original query that "selects" the data to send in that primary response
    /// once the plan in `node` completes). Note that if the parent `DeferNode` is nested, then it
    /// must come inside the `DeferredNode` in which it is nested, and in that case this
    /// sub-selection will start at that parent `DeferredNode.query_path`. Note that this can be
    /// `None` in the rare case that everything in the original query is deferred (which is not very
    /// useful  in practice, but not disallowed by the @defer spec at the moment).
    pub sub_selection: Option<String>,
    /// The plan to get all the data for the primary block. Same notes as for subselection: usually
    /// defined, but can be undefined in some corner cases where nothing is to be done in the
    /// primary block.
    pub node: Option<Box<PlanNode>>,
}

/// A deferred block of a `DeferNode`.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct DeferredDeferBlock {
    /// References one or more fetch node(s) (by `id`) within `DeferNode.primary.node`. The plan of
    /// this deferred part should not be started until all such fetches return.
    pub depends: Vec<DeferredDependency>,
    /// The optional defer label.
    pub label: Option<String>,
    /// Path, in the query, to the `@defer` application this corresponds to. The `sub_selection`
    /// starts at this `query_path`.
    pub query_path: Vec<QueryPathElement>,
    /// The part of the original query that "selects" the data to send in the deferred response
    /// (once the plan in `node` completes). Will be set _unless_ `node` is a `DeferNode` itself.
    pub sub_selection: Option<String>,
    /// The plan to get all the data for this deferred block. Usually set, but can be `None` for a
    /// `@defer` application where everything has been fetched in the "primary block" (i.e. when
    /// this deferred block only exists to expose what should be send to the upstream client in a
    /// deferred response), but without declaring additional fetches. This happens for @defer
    /// applications that cannot be handled through the query planner and where the defer cannot be
    /// passed through to the subgraph).
    pub node: Option<Box<PlanNode>>,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct DeferredDependency {
    /// A `FetchNode` ID.
    pub id: String,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct ConditionNode {
    pub condition_variable: Name,
    pub if_clause: Option<Box<PlanNode>>,
    pub else_clause: Option<Box<PlanNode>>,
}

/// The type of rewrites currently supported on the input/output data of fetches.
///
/// A rewrite usually identifies some sub-part of the data and some action to perform on that
/// sub-part.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, derive_more::From)]
pub enum FetchDataRewrite {
    ValueSetter(FetchDataValueSetter),
    KeyRenamer(FetchDataKeyRenamer),
}

/// A rewrite that sets a value at the provided path of the data it is applied to.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FetchDataValueSetter {
    /// Path to the value that is set by this "rewrite".
    pub path: Vec<FetchDataPathElement>,
    /// The value to set at `path`. Note that the query planner currently only uses string values,
    /// but that may change in the future.
    pub set_value_to: serde_json_bytes::Value,
}

/// A rewrite that renames the key at the provided path of the data it is applied to.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FetchDataKeyRenamer {
    /// Path to the key that is renamed by this "rewrite".
    pub path: Vec<FetchDataPathElement>,
    /// The key to rename to at `path`.
    pub rename_key_to: Name,
}

/// Vectors of this element match path(s) to a value in fetch data. Each element is (1) a key in
/// object data, (2) _any_ index in array data (often serialized as `@`), (3) a typename constraint
/// on the object data at that point in the path(s) (a path should only match for objects whose
/// `__typename` is the provided type), or (4) a parent indicator to move upwards one level in the
/// object.
///
/// It's possible for vectors of this element to match no paths in fetch data, e.g. if an object key
/// doesn't exist, or if an object's `__typename` doesn't equal the provided one. If this occurs,
/// then query plan execution should not execute the instruction this path is associated with.
///
/// The path starts at the top of the data it is applied to. So for instance, for fetch data inputs,
/// the path starts at the root of the object representing those inputs.
///
/// Note that the `@` is currently optional in some contexts, as query plan execution may assume
/// upon encountering array data in a path that it should match the remaining path to the array's
/// elements.
#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
pub enum FetchDataPathElement {
    Key(Name, Option<Conditions>),
    AnyIndex(Option<Conditions>),
    TypenameEquals(Name),
    Parent,
}

pub type Conditions = Vec<Name>;

/// Vectors of this element match a path in a query. Each element is (1) a field in a query, or (2)
/// an inline fragment in a query.
#[derive(Debug, Clone, PartialEq, serde::Serialize, Deserialize)]
pub enum QueryPathElement {
    Field { response_key: Name },
    InlineFragment { type_condition: Name },
}

impl PlanNode {
    /// Returns the kind of plan node this is as a human-readable string. Exact output not guaranteed.
    fn node_kind(&self) -> &'static str {
        match self {
            Self::Fetch(_) => "Fetch",
            Self::Sequence(_) => "Sequence",
            Self::Parallel(_) => "Parallel",
            Self::Flatten(_) => "Flatten",
            Self::Defer(_) => "Defer",
            Self::Condition(_) => "Condition",
        }
    }
}