Module expr

Expand description

Typed expression AST (Django Q / F / lookup equivalents).

Expressions are pure data: building them never performs I/O. Backends compile them into their own dialect.

Two layers exist:

Expr: untyped tree stored inside a QueryPlan.
Field<M, T>: a typed column handle. The Model derive generates one associated constant per field (User::name), so lookups are checked at compile time: icontains exists only on text fields, comparison values must convert into the field’s type. Calc (arithmetic results) and Joined (fields reached through a foreign key) offer the same lookups.

Function, aggregate and window constructors live in functions, Count/Sum/… and RowNumber/Rank/….

Re-exports§

Aggregate: An aggregate call: function, argument, DISTINCT and FILTER (WHERE ..).
ArrayAgg: Collect values into an array (PostgreSQL only).
Avg: AVG(expr).
Calc: Result of arithmetic on typed handles: an expression that is still known to have type T, so it can be compared with and assigned to T fields.
Column: A (optionally source-qualified) column reference.
Count: COUNT(*) and COUNT(expr).
CumeDist: CUME_DIST().
DenseRank: DENSE_RANK().
Field: Typed column handle for model M whose Rust type is T.
FirstValue: FIRST_VALUE(expr).
Joined: A column of a related model, usable like a field of the root model M.
Lag: LAG(expr, offset).
LastValue: LAST_VALUE(expr).
Lead: LEAD(expr, offset).
Max: MAX(expr).
Min: MIN(expr).
Ntile: NTILE(n).
PercentRank: PERCENT_RANK().
Rank: RANK().
RelHop: One foreign-key hop: <parent>.<fk_column> = <table>.<pk_column>.
RelatedColumn: A column of a related model, addressed by its foreign-key path.
RowNumber: ROW_NUMBER().
StdDev: Standard deviation (PostgreSQL only).
StringAgg: Join text values with a separator (STRING_AGG on PostgreSQL, group_concat on SQLite).
Sum: SUM(expr). NULL for an empty group; PostgreSQL returns numeric for integer sums.
Variance: Variance (PostgreSQL only).
Window: A window function with its PARTITION BY and ORDER BY.

AggFunc: The aggregate function computed.
BinaryOp: Binary operators: comparisons, boolean connectives and arithmetic.
Expr: Expression tree node.
Lookup: Lookups that are not plain binary comparisons.
UnaryOp: Unary operators.
WindowFunc: The function evaluated over the window.

DateLike: Column types that have a calendar date (year, month, …).
FkSlot: A foreign-key slot of a model struct: ForeignKey<T> or Option<ForeignKey<T>>.
Literal: A literal value that can stand for a T column (no column references), used by is_in and range.
Numeric: Column types that support arithmetic.
Operand: A value that can stand for a T column in a comparison or assignment: a T, a T for an Option<T> column, a primary key or model reference for a foreign key, or another typed handle of type T.
Related: Column of related model T that can be reached through more hops: a Field of T, or a Joined handle already rooted at T.
TextLike: Text column types (icontains, starts_with, …).
TimeLike: Column types that have a time of day (hour, minute, second).