Advanced Operations

Field Manual Section 7 - Tactical Coordination

In the field, isolated units rarely win the battle. Coordination is key. Joins let you link data across tables like synchronized squads advancing under fire. In Tank, a join is a first class DataSet, just like a TableRef. That means you can call select() and then, filter, map, reduce, etc, using the same composable Stream API you already know.

Schema In Play

Continuing with the Operator and RadioLog schema introduce earlier. The following examples show more advanced query capabilities, something that go beyour simple CRUD operations shown earlier but still without revolving to raw sql.

Rust

#[derive(Entity)]
#[tank(schema = "operations", name = "radio_operator")]
pub struct Operator {
    #[tank(primary_key)]
    pub id: Uuid,
    pub callsign: String,
    #[tank(name = "rank")]
    pub service_rank: String,
    #[tank(name = "enlistment_date")]
    pub enlisted: Date,
    pub is_certified: bool,
}

#[derive(Entity)]
#[tank(schema = "operations")]
pub struct RadioLog {
    #[tank(primary_key)]
    pub id: Uuid,
    #[tank(references = Operator::id)]
    pub operator: Uuid,
    pub message: String,
    pub unit_callsign: String,
    #[tank(name = "tx_time")]
    pub transmission_time: OffsetDateTime,
    #[tank(name = "rssi")]
    pub signal_strength: i8,
}

SQL

CREATE TABLE IF NOT EXISTS operations.radio_operator (
    id UUID PRIMARY KEY,
    callsign VARCHAR NOT NULL,
    rank VARCHAR NOT NULL,
    enlistment_date DATE NOT NULL,
    is_certified BOOLEAN NOT NULL);

CREATE TABLE IF NOT EXISTS operations.radio_log (
    id UUID PRIMARY KEY,
    operator UUID NOT NULL REFERENCES operations.radio_operator(id),
    message VARCHAR NOT NULL,
    unit_callsign VARCHAR NOT NULL,
    tx_time TIMESTAMP WITH TIME ZONE NOT NULL,
    rssi TINYINT NOT NULL);

Data

Operators:

callsign	rank	enlisted	is_certified
SteelHammer	Major	2015-06-20	✅ true
Viper	Sgt	2019-11-01	✅ true
Rook	Pvt	2023-01-15	❌ false

Radio logs:

message	unit_callsign	tx_time	rssi
Radio check, channel 3. How copy?	Alpha-1	2025-11-04T19:45:21+01	−42
Target acquired. Requesting coordinates.	Alpha-1	2025-11-04T19:54:12+01	−55
Heavy armor spotted, grid 4C.	Alpha-1	2025-11-04T19:51:09+01	−52
Perimeter secure. All clear.	Bravo-2	2025-11-04T19:51:09+01	−68
Radio check, grid 1A. Over.	Charlie-3	2025-11-04T18:59:11+02	−41
Affirmative, engaging.	Alpha-1	2025-11-03T23:11:54+00	−54

Selecting & Ordering

Here is a minimal example illustrating the use of tank::cols!() which supports aliasing and ordering, alternatively if those features are not used, a more terse syntax is possible: [RadioLog::signal_strength, Operator::callsign, RadioLog::message] or Entity::columns(). Strongest certified transmissions:

let messages = join!(
    Operator JOIN RadioLog ON Operator::id == RadioLog::operator
)
.select(
    executor,
    cols!(
        RadioLog::signal_strength as strength DESC,
        Operator::callsign ASC,
        RadioLog::message,
    ),
    &expr!(Operator::is_certified && RadioLog::message != "Radio check%" as LIKE),
    Some(100),
)
.map(|row| {
    row.and_then(|row| {
        #[derive(Entity)]
        struct Row {
            message: String,
            callsign: String,
        }
        Row::from_row(row).and_then(|row| Ok((row.message, row.callsign)))
    })
})
.try_collect::<Vec<_>>()
.await?;
assert!(
    messages.iter().map(|(a, b)| (a.as_str(), b.as_str())).eq([
        ("Heavy armor spotted, grid 4C.", "SteelHammer"),
        ("Affirmative, engaging.", "SteelHammer"),
        ("Target acquired. Requesting coordinates.", "SteelHammer"),
        ("Perimeter secure. All clear.", "Viper"),
    ]
    .into_iter())
);

Expr

Cols

tank::cols!(col, ...) macro is more expressive syntax to select columns in a query, it supports:

• Entity::column
• Entity::column as name (aliasing)
• Entity::column + 1 (expressions)
• SUM(Entity::column) (function calls)
• COUNT(*) (function calls)
• * (wildcard)
• COUNT(*) (function calls)
• schema.table.column
• Entity::column DESC (ordering)
• SUM(Entity::column + table.column) as total DESC (a combination)

Performance Notes

• Request only the necessary columns.
• Stream + early break for threshold scans (do not SELECT COUNT then SELECT data).
• Prepared joins: stabilize SQL for hot loops.
• Alias recurrent long names (micro but accumulative in tight loops).
• Prefer limits (Some(n)) when you are sampling or confirming existence.

Edge / Failure Signals

• Referencing a non-joined table column: immediate construction error (fast feedback).
• Duplicate alias: conflict error (prevents silent shadowing).
• LEFT join + non-Option decode on NULL: conversion error (fix by making field optional).
• Type mismatch in from_row: bubbles as Err, surface early in tests.
• Unused prepared parameter (bind count mismatch): error before execution.

Units in position. Advance. Tank out.