Trait AppearsInFromClause 

pub trait AppearsInFromClause<QS> {
    type Count;
}

Determines how many times QS appears in Self

This trait is primarily used to determine whether or not a column is selectable from a given from clause. A column can be selected if its table appears in the from clause exactly once.

We do not allow the same table to appear in a query multiple times in any context where referencing that table would be ambiguous (depending on the context and backend being used, this may or may not be something that would otherwise result in a runtime error).

Required Associated Types

type Count

How many times does QS appear in Self?

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl<From, T> AppearsInFromClause<T> for SelectStatement<From>

where From: AsQuerySource, From::QuerySource: AppearsInFromClause<T> + QuerySource,

Allow SelectStatement<From> to act as if it were From as long as no other query methods have been called on it

type Count = <<From as AsQuerySource>::QuerySource as AppearsInFromClause<T>>::Count

impl<S, QS> AppearsInFromClause<QS> for Alias<S>

where S: AliasSource, S::Target: AliasAppearsInFromClause<S, QS>,

type Count = <<S as AliasSource>::Target as AliasAppearsInFromClause<S, QS>>::Count

impl<StmtKind, T1, T2> AppearsInFromClause<T1> for ReturningQuerySource<StmtKind, T2>

where T1: TableNotEqual<T2> + QueryRelation, T2: QueryRelation,

Available on crate feature i-implement-a-third-party-backend-and-opt-into-breaking-changes only.

type Count = Never

impl<StmtKind, T> AppearsInFromClause<OldIdent> for ReturningQuerySource<StmtKind, T>

Available on crate feature i-implement-a-third-party-backend-and-opt-into-breaking-changes only.

There is an old. or old_value() in ReturningQuerySource<UpdateStmt, T>

Useful to check non-ambiguity of old or old_value

type Count = Once

impl<T1, T2> AppearsInFromClause<T2> for T1

where T1: TableNotEqual<T2> + QueryRelation, T2: QueryRelation,

type Count = Never

impl<T> AppearsInFromClause<OldIdent> for T

where T: QueryRelation,

Available on crate feature i-implement-a-third-party-backend-and-opt-into-breaking-changes only.

There isn’t one directly on tables (this is useful for typechecking old or old_value in subqueries in returning)

type Count = Never

impl<T> AppearsInFromClause<ReturningQuerySource<OldIdent, T>> for ReturningQuerySource<InsertStmtWithOnConflictDoUpdate, T>

Available on crate feature i-implement-a-third-party-backend-and-opt-into-breaking-changes only.

There is an old. or old_value for T in ReturningQuerySource<InsertStmtWithOnConflictDoUpdate, T>

type Count = Once

impl<T> AppearsInFromClause<ReturningQuerySource<OldIdent, T>> for ReturningQuerySource<UpdateStmt, T>

Available on crate feature i-implement-a-third-party-backend-and-opt-into-breaking-changes only.

There is an old. or old_value for T in ReturningQuerySource<UpdateStmt, T>

type Count = Once