Enum ProjectList

pub enum ProjectList {
    Name(Vec<ProjectName>),
    List(Vec<RelExpr>, Vec<(Box<str>, FieldProject)>),
    Limit(Box<ProjectList>, u64),
    Agg(Vec<RelExpr>, AggType, Box<str>, AlgebraicType),
}

A projection is the root of any relational expression. This type represents a projection that returns fields.

For example:

select a, b from t

and

select t.a as x from t join s ...

Note that RLS takes a single expression and produces a list of expressions. Hence why these variants take lists rather than single expressions.

Why does RLS take an expression and produce a list?

There may be multiple RLS rules associated to a single table. Semantically these rules represent a UNION over that table, and this corresponds to a UNION in the original expression.

TODO: We should model the UNION explicitly in the physical plan.

Ex.

Let’s say we have the following rules for the users table:

use spacetimedb::client_visibility_filter;
use spacetimedb::Filter;

#[client_visibility_filter]
const USER_FILTER: Filter = Filter::Sql(
    "SELECT users.* FROM users WHERE identity = :sender"
);

#[client_visibility_filter]
const ADMIN_FILTER: Filter = Filter::Sql(
    "SELECT users.* FROM users JOIN admins"
);

The user query

SELECT * FROM users WHERE level > 5

essentially resolves to

SELECT users.*
FROM users
WHERE identity = :sender AND level > 5

UNION ALL

SELECT users.*
FROM users JOIN admins
WHERE users.level > 5

Variants

Name(Vec<ProjectName>)

List(Vec<RelExpr>, Vec<(Box<str>, FieldProject)>)

Limit(Box<ProjectList>, u64)

Agg(Vec<RelExpr>, AggType, Box<str>, AlgebraicType)

Implementations

impl ProjectList

pub fn return_table(&self) -> Option<&TableSchema>

Does this expression project a single relvar? If so, we return it’s TableSchema. If not, it projects a list of columns, so we return None.

pub fn return_table_id(&self) -> Option<TableId>

Does this expression project a single relvar? If so, we return it’s TableId. If not, it projects a list of columns, so we return None.

pub fn for_each_return_field(&self, f: impl FnMut(&str, &AlgebraicType))

Iterate over the projected column names and types

Trait Implementations

impl Debug for ProjectList

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.