colouring-montreal/app/src/building.js

/**
 * Building data access
 *
 */
import db from './db';
// data type note: PostgreSQL bigint (64-bit) is handled as string in JavaScript, because of
// JavaScript numerics are 64-bit double, giving only partial coverage.

const TransactionMode = db.$config.pgp.txMode.TransactionMode;
const isolationLevel = db.$config.pgp.txMode.isolationLevel;

// Create a transaction mode (serializable, read-write):
const serializable = new TransactionMode({
    tiLevel: isolationLevel.serializable,
    readOnly: false
});

function queryBuildingsAtPoint(lng, lat) {
    return db.manyOrNone(
        `SELECT b.*
        FROM buildings as b, geometries as g
        WHERE
            b.geometry_id = g.geometry_id
        AND
            ST_Intersects(
                ST_Transform(
                    ST_SetSRID(ST_Point($1, $2), 4326),
                    3857
                ),
                geometry_geom
            )
        `,
        [lng, lat]
    ).catch(function(error){
        console.error(error);
        return undefined;
    });
}

function queryBuildingsByReference(key, id) {
    if (key === 'toid'){
        return db.manyOrNone(
            "SELECT * FROM buildings WHERE b.ref_toid = $1",
            [id]
        ).catch(function(error){
            console.error(error);
            return undefined;
        });
    }
    if (key === 'uprn') {
        return db.manyOrNone(
            `SELECT b.*
            FROM buildings as b, building_properties as p
            WHERE
                b.building_id = p.building_id
            AND
                p.uprn = $1
            `,
            [id]
        ).catch(function(error){
            console.error(error);
            return undefined;
        });
    }
    return {error: 'Key must be UPRN or TOID'};
}

function getBuildingById(id) {
    return db.one(
        "SELECT * FROM buildings WHERE building_id = $1",
        [id]
    ).catch(function(error){
        console.error(error);
        return undefined;
    });
}

function saveBuilding(building_id, building, user_id) {
    // save building must fail if the revision seen by the user != the latest revision
    // - any 'intuitive' retries to be handled by clients of this code
    // revision id allows for a long user 'think time' between view-building, update-building
    // (optimistic locking implemented using field-based row versioning)
    const previous_revision_id = building.revision_id;

    // remove read-only fields from consideration
    delete building.building_id;
    delete building.revision_id;
    delete building.geometry_id;

    // start transaction around save operation
    // - select and compare to identify changeset
    // - insert changeset
    // - update to latest state
    // commit or rollback (repeated-read sufficient? or serializable?)
    return db.tx(t => {
        const check_revision = (previous_revision_id)? "and revision_id = $2" : "";
        return t.one(
            `SELECT * FROM buildings WHERE building_id = $1 ${check_revision} FOR UPDATE;`,
            [building_id, previous_revision_id]
        ).then(old_building => {
            const patches = compare(old_building, building, BUILDING_FIELD_WHITELIST);
            const forward = patches[0];
            const reverse = patches[1];
            return t.one(
                `INSERT INTO logs (
                    forward_patch, reverse_patch, building_id, user_id
                ) VALUES (
                    $1:json, $2:json, $3, $4
                ) RETURNING log_id
                `,
                [forward, reverse, building_id, user_id]
            ).then(revision => {
                const sets = db.$config.pgp.helpers.sets(forward);
                const check_revision = (previous_revision_id)? "AND revision_id = $4" : "";
                return t.one(
                    `UPDATE
                        buildings
                    SET
                        revision_id = $1,
                        $2:raw
                    WHERE
                        building_id = $3 ${check_revision}
                    RETURNING
                        *
                    `,
                    [revision.log_id, sets, building_id, previous_revision_id]
                )
            });
        });
    }).catch(function(error){
        // TODO report transaction error as 'Need to re-fetch building before update'
        console.error(error);
        return undefined;
    });
}


function likeBuilding(building_id, user_id) {
    // start transaction around save operation
    // - insert building-user like
    // - count total likes
    // - insert changeset
    // - update building to latest state
    // commit or rollback (serializable - could be more compact?)
    return db.tx({serializable}, t => {
        return t.none(
            "INSERT INTO building_user_likes ( building_id, user_id ) VALUES ($1, $2);",
            [building_id, user_id]
        ).then(() => {
            return t.one(
                "SELECT count(*) as likes FROM building_user_likes WHERE building_id = $1;",
                [building_id]
            ).then(building => {
                return t.one(
                    `INSERT INTO logs (
                        forward_patch, building_id, user_id
                    ) VALUES (
                        $1:jsonb, $2, $3
                    ) RETURNING log_id
                    `,
                    [{likes_total: building.likes}, building_id, user_id]
                ).then(revision => {
                    return t.one(
                        `UPDATE buildings
                        SET
                            revision_id = $1,
                            likes_total = $2
                        WHERE
                            building_id = $3
                        RETURNING
                            *
                        `,
                        [revision.log_id, building.likes, building_id]
                    )
                })
            });
        });
    }).catch(function(error){
        // TODO report transaction error as 'Need to re-fetch building before update'
        console.error(error);
        return undefined;
    });
}

const BUILDING_FIELD_WHITELIST = new Set([
    'ref_toid',
    'ref_osm_id',
    'location_name',
    'location_number',
    'location_street',
    'location_line_two',
    'location_town',
    'location_postcode',
    'location_latitude',
    'location_longitude',
    'date_year',
    'date_lower',
    'date_upper',
    'date_source',
    'facade_year',
    'facade_upper',
    'facade_lower',
    'facade_source',
    'size_storeys_attic',
    'size_storeys_core',
    'size_storeys_basement',
    'size_height_apex',
    'size_floor_area_ground',
    'size_floor_area_total',
    'size_width_frontage',
]);

/**
 * Compare old and new data objects, generate shallow merge patch of changed fields
 * - forward patch is object with {keys: new_values}
 * - reverse patch is object with {keys: old_values}
 *
 * @param {object} old_obj
 * @param {object} new_obj
 * @param {Set} whitelist
 * @returns {[object, object]}
 */
function compare(old_obj, new_obj, whitelist){
    const reverse_patch = {}
    const forward_patch = {}
    for (const [key, value] of Object.entries(new_obj)) {
        if (old_obj[key] !== value && whitelist.has(key)) {
            reverse_patch[key] = old_obj[key];
            forward_patch[key] = value;
        }
    }
    return [forward_patch, reverse_patch]
}

export { queryBuildingsAtPoint, queryBuildingsByReference, getBuildingById, saveBuilding,
         likeBuilding };