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use std::fmt;
use crate::backend::{Backend, HasBindCollector};
use crate::query_builder::{BindCollector, QueryBuilder};
use crate::result::QueryResult;
use crate::serialize::ToSql;
use crate::sql_types::HasSqlType;
#[allow(missing_debug_implementations)]
/// The primary type used when walking a Diesel AST during query execution.
///
/// Executing a query is generally done in multiple passes. This list includes,
/// but is not limited to:
///
/// - Generating the SQL
/// - Collecting and serializing bound values (sent separately from the SQL)
/// - Determining if a query is safe to store in the prepared statement cache
///
/// When adding a new type that is used in a Diesel AST, you don't need to care
/// about which specific passes are being performed, nor is there any way for
/// you to find out what the current pass is. You should simply call the
/// relevant methods and trust that they will be a no-op if they're not relevant
/// to the current pass.
pub struct AstPass<'a, 'b, DB>
where
DB: Backend,
DB::QueryBuilder: 'a,
<DB as HasBindCollector<'a>>::BindCollector: 'a,
DB::MetadataLookup: 'a,
'b: 'a,
{
internals: AstPassInternals<'a, 'b, DB>,
backend: &'b DB,
}
impl<'a, 'b, DB> AstPass<'a, 'b, DB>
where
DB: Backend,
'b: 'a,
{
pub(crate) fn to_sql(
query_builder: &'a mut DB::QueryBuilder,
options: &'a mut AstPassToSqlOptions,
backend: &'b DB,
) -> Self {
AstPass {
internals: AstPassInternals::ToSql(query_builder, options),
backend,
}
}
pub(crate) fn collect_binds(
collector: &'a mut <DB as HasBindCollector<'b>>::BindCollector,
metadata_lookup: &'a mut DB::MetadataLookup,
backend: &'b DB,
) -> Self {
AstPass {
internals: AstPassInternals::CollectBinds {
collector,
metadata_lookup,
},
backend,
}
}
pub(crate) fn is_safe_to_cache_prepared(result: &'a mut bool, backend: &'b DB) -> Self {
AstPass {
internals: AstPassInternals::IsSafeToCachePrepared(result),
backend,
}
}
pub(crate) fn debug_binds(formatter: &'a mut Vec<&'b dyn fmt::Debug>, backend: &'b DB) -> Self {
AstPass {
internals: AstPassInternals::DebugBinds(formatter),
backend,
}
}
/// Does running this AST pass have any effect?
///
/// The result will be set to `false` if any method that generates SQL
/// is called.
pub(crate) fn is_noop(result: &'a mut bool, backend: &'b DB) -> Self {
AstPass {
internals: AstPassInternals::IsNoop(result),
backend,
}
}
#[cfg(feature = "sqlite")]
pub(crate) fn skip_from(&mut self, value: bool) {
if let AstPassInternals::ToSql(_, ref mut options) = self.internals {
options.skip_from = value
}
}
/// Call this method whenever you pass an instance of `AstPass` by value.
///
/// Effectively copies `self`, with a narrower lifetime. When passing a
/// reference or a mutable reference, this is normally done by rust
/// implicitly. This is why you can pass `&mut Foo` to multiple functions,
/// even though mutable references are not `Copy`. However, this is only
/// done implicitly for references. For structs with lifetimes it must be
/// done explicitly. This method matches the semantics of what Rust would do
/// implicitly if you were passing a mutable reference
pub fn reborrow(&'_ mut self) -> AstPass<'_, 'b, DB> {
let internals = match self.internals {
AstPassInternals::ToSql(ref mut builder, ref mut options) => {
AstPassInternals::ToSql(&mut **builder, &mut **options)
}
AstPassInternals::CollectBinds {
ref mut collector,
ref mut metadata_lookup,
} => AstPassInternals::CollectBinds {
collector: &mut **collector,
metadata_lookup: &mut **metadata_lookup,
},
AstPassInternals::IsSafeToCachePrepared(ref mut result) => {
AstPassInternals::IsSafeToCachePrepared(&mut **result)
}
AstPassInternals::DebugBinds(ref mut f) => AstPassInternals::DebugBinds(&mut **f),
AstPassInternals::IsNoop(ref mut result) => AstPassInternals::IsNoop(&mut **result),
};
AstPass {
internals,
backend: self.backend,
}
}
/// Mark the current query being constructed as unsafe to store in the
/// prepared statement cache.
///
/// Diesel caches prepared statements as much as possible. However, it is
/// important to ensure that this doesn't result in unbounded memory usage
/// on the database server. To ensure this is the case, any logical query
/// which could generate a potentially unbounded number of prepared
/// statements *must* call this method. Examples of AST nodes which do this
/// are:
///
/// - `SqlLiteral`. We have no way of knowing if the SQL string was
/// constructed dynamically or not, so we must assume it was dynamic.
/// - `EqAny` when passed a Rust `Vec`. The `IN` operator requires one bind
/// parameter per element, meaning that the query could generate up to
/// `usize` unique prepared statements.
/// - `InsertStatement`. Unbounded due to the variable number of records
/// being inserted generating unique SQL.
/// - `UpdateStatement`. The number of potential queries is actually
/// technically bounded, but the upper bound is the number of columns on
/// the table factorial which is too large to be safe.
pub fn unsafe_to_cache_prepared(&mut self) {
if let AstPassInternals::IsSafeToCachePrepared(ref mut result) = self.internals {
**result = false
}
}
/// Push the given SQL string on the end of the query being constructed.
///
/// # Example
///
/// ```rust
/// # use diesel::query_builder::{QueryFragment, AstPass};
/// # use diesel::backend::Backend;
/// # use diesel::QueryResult;
/// # struct And<Left, Right> { left: Left, right: Right }
/// impl<Left, Right, DB> QueryFragment<DB> for And<Left, Right>
/// where
/// DB: Backend,
/// Left: QueryFragment<DB>,
/// Right: QueryFragment<DB>,
/// {
/// fn walk_ast<'b>(&'b self, mut out: AstPass<'_, 'b, DB>) -> QueryResult<()> {
/// self.left.walk_ast(out.reborrow())?;
/// out.push_sql(" AND ");
/// self.right.walk_ast(out.reborrow())?;
/// Ok(())
/// }
/// }
/// # fn main() {}
/// ```
pub fn push_sql(&mut self, sql: &str) {
match self.internals {
AstPassInternals::ToSql(ref mut builder, _) => builder.push_sql(sql),
AstPassInternals::IsNoop(ref mut result) => **result = false,
_ => {}
}
}
/// Push the given SQL identifier on the end of the query being constructed.
///
/// The identifier will be quoted using the rules specific to the backend
/// the query is being constructed for.
pub fn push_identifier(&mut self, identifier: &str) -> QueryResult<()> {
match self.internals {
AstPassInternals::ToSql(ref mut builder, _) => builder.push_identifier(identifier)?,
AstPassInternals::IsNoop(ref mut result) => **result = false,
_ => {}
}
Ok(())
}
/// Push a value onto the given query to be sent separate from the SQL
///
/// This method affects multiple AST passes. It should be called at the
/// point in the query where you'd want the parameter placeholder (`$1` on
/// PG, `?` on other backends) to be inserted.
pub fn push_bind_param<T, U>(&mut self, bind: &'b U) -> QueryResult<()>
where
DB: HasSqlType<T>,
U: ToSql<T, DB>,
{
match self.internals {
AstPassInternals::ToSql(ref mut out, _) => out.push_bind_param(),
AstPassInternals::CollectBinds {
ref mut collector,
ref mut metadata_lookup,
} => collector.push_bound_value(bind, metadata_lookup)?,
AstPassInternals::DebugBinds(ref mut f) => {
f.push(bind);
}
AstPassInternals::IsNoop(ref mut result) => **result = false,
_ => {}
}
Ok(())
}
pub(crate) fn push_bind_param_value_only<T, U>(&mut self, bind: &'b U) -> QueryResult<()>
where
DB: HasSqlType<T>,
U: ToSql<T, DB>,
{
match self.internals {
AstPassInternals::CollectBinds { .. } | AstPassInternals::DebugBinds(..) => {
self.push_bind_param(bind)?
}
AstPassInternals::ToSql(ref mut out, _) => {
out.push_bind_param_value_only();
}
_ => {}
}
Ok(())
}
/// Get information about the backend that will consume this query
#[cfg_attr(
not(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"),
doc(hidden)
)] // This is used by the `sql_function` macro
#[cfg_attr(
doc_cfg,
doc(cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"))
)]
pub fn backend(&self) -> &DB {
self.backend
}
/// Get if the query should be rendered with from clauses or not
#[cfg_attr(
not(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"),
doc(hidden)
)] // This is used by the `__diesel_column` macro
#[cfg_attr(
doc_cfg,
doc(cfg(feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"))
)]
pub fn should_skip_from(&self) -> bool {
if let AstPassInternals::ToSql(_, ref options) = self.internals {
options.skip_from
} else {
false
}
}
}
#[allow(missing_debug_implementations)]
/// This is separate from the struct to cause the enum to be opaque, forcing
/// usage of the methods provided rather than matching on the enum directly.
/// This essentially mimics the capabilities that would be available if
/// `AstPass` were a trait.
enum AstPassInternals<'a, 'b, DB>
where
DB: Backend,
DB::QueryBuilder: 'a,
<DB as HasBindCollector<'a>>::BindCollector: 'a,
DB::MetadataLookup: 'a,
'b: 'a,
{
ToSql(&'a mut DB::QueryBuilder, &'a mut AstPassToSqlOptions),
CollectBinds {
collector: &'a mut <DB as HasBindCollector<'b>>::BindCollector,
metadata_lookup: &'a mut DB::MetadataLookup,
},
IsSafeToCachePrepared(&'a mut bool),
DebugBinds(&'a mut Vec<&'b dyn fmt::Debug>),
IsNoop(&'a mut bool),
}
#[diesel_derives::__diesel_public_if(
feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"
)]
#[allow(missing_debug_implementations)]
#[allow(missing_copy_implementations)]
#[derive(Default)]
/// This is used to pass down additional settings to the `AstPass`
/// when rendering the sql string.
pub(crate) struct AstPassToSqlOptions {
skip_from: bool,
}