Crate pg_named_args 

This library allows one to use named arguments in PostgreSQL queries. This library is especially aimed at supporting rust-postgres. A macro is provided to rewrite queries with named arguments, into a query and its positional arguments.

Query Argument Syntax

The macro uses struct syntax for the named arguments. The struct name Args is required to support rustfmt and rust-analyzer. As can be seen from the example below, shorthand field initialization is also allowed for named arguments.

let location = "netherlands";
let period = Period {
    start: 2020,
    end: 2030,
};

let (query, args) = query_args!(
    r"
    SELECT location, time, report
    FROM weather_reports
    WHERE location = $location
        AND time BETWEEN $start AND $end
    ORDER BY location, time DESC
    ",
    Args {
        location,
        start: period.start,
        end: period.end,
    }
);

let rows = client.query(query, args).await?;

This expands to the equivalent of

let (query, args) = (
    r"
    SELECT location, time, report
    FROM weather_reports
    WHERE location = $1
        AND time BETWEEN $2 AND $3
    ORDER BY location, time DESC
    ",
    &[&location, &period.start, &period.end]
);

Insert Syntax

For INSERT’s a special syntax is supported, which helps to avoid mismatches between the list of column names and the values:

let location = "sweden";
let time = "monday";
let report = "sunny";

let (query, args) = query_args!(
    r"
    INSERT INTO weather_reports
        ( $[location, time, report] )
    VALUES
        ( $[..] )
    ",
    Args {
        location,
        time,
        report
    }
);

client.execute(query, args).await?;

The SQL would be

INSERT INTO weather_reports
    ( location, time, report )
VALUES
    ( $1, $2, $3 )

Optional Parameter Syntax

When doing updates it can be useful to dynamically build SQL.

This is essential when for example a column must sometimes be updated, but the column is also nullable. To differentiate between those cases, pg_named_args adds a Update<T> type which has the Update::Yes(val) and Update::No variants. This type can be combined with the Option type as Update<Option<T>>.

The syntax to use optional parameter is like this:

fn update_report(id: i64, report: Update<Option<&str>>) {
    let (query, args) = query_args!(
        r"
        UPDATE weather_reports
        SET $[report?] = $[..]
        WHERE id = $id
        ",
        Args {
            report,
            id,
        }
    );
}

// Don't update the report.
update_report(0, Update::No);
// Set the report to `null`.
update_report(1, Update::Yes(None));
// Set the report to "sunny".
update_report(2, Update::Yes(Some("sunny")));

The SQL would be

UPDATE weather_reports
SET report = CASE WHEN $1 THEN $2 ELSE report END
WHERE id = $3

The optional parameter has been desugared to two parameters, one to indicate if the value should be updated and another parameter with the new value.

Note that it is not possible to use the same argument with and without the ? modifier in the same query.

Fragment Syntax

let select = fragment!("
    SELECT location, time, report
    FROM weather_reports
");

let location = "sweden";

let (query, args) = query_args!(
    r"
    ${select}
    WHERE location = $location
    ",
    Args {
        // Temporary lifetime extension doesn't work when fragments are involved,
        // so we have to borrow the parameter here.
        location: &location,
    },
    Sql {
        select,
    }
);

The SQL would be

SELECT location, time, report
FROM weather_reports
WHERE location = $1

IDE Support

First, the syntax used by this macro is compatible with rustfmt. Run rustfmt as you would normally and it will format the macro.

Second, the macro is implemented in a way that is rust-analyzer “friendly”. This means that rust-analyzer knows which arguments are required and can complete them. Use the code action “Fill struct fields” or ask rust-analyzer to complete a field name.

Macros

fragment

This macro creates a Fragment from a string literal.

query_args

The macro returns a tuple containing the query and the parameter slice that can be used to call the various query methods provided by rust_postgres/tokio_postgres.

Structs

Fragment

Helper type to safely build queries from string literals.

Enums

Update

This enum is used for optional arguments.