Count related records with Sequelize

Question

I have two tables, locationsand sensors. Each entry in sensorshas a foreign key pointing to locations. Using Sequelize, how do I get all entries from locationsand the total number of entries in sensorsthat are associated with each entry in locations?

Raw SQL:

SELECT 
    `locations`.*,
    COUNT(`sensors`.`id`) AS `sensorCount` 
FROM `locations` 
JOIN `sensors` ON `sensors`.`location`=`locations`.`id`;
GROUP BY `locations`.`id`;

Models:

module.exports = function(sequelize, DataTypes) {
    var Location = sequelize.define("Location", {
        id: {
            type: DataTypes.INTEGER.UNSIGNED,
            primaryKey: true
        },
        name: DataTypes.STRING(255)
    }, {
        classMethods: {
            associate: function(models) {
                Location.hasMany(models.Sensor, {
                    foreignKey: "location"
                });
            }
        }
    });

    return Location;
};


module.exports = function(sequelize, DataTypes) {
    var Sensor = sequelize.define("Sensor", {
        id: {
            type: DataTypes.INTEGER.UNSIGNED,
            primaryKey: true
        },
        name: DataTypes.STRING(255),
        type: {
            type: DataTypes.INTEGER.UNSIGNED,
            references: {
                model: "sensor_types",
                key: "id"
            }
        },
        location: {
            type: DataTypes.INTEGER.UNSIGNED,
            references: {
                model: "locations",
                key: "id"
            }
        }
    }, {
        classMethods: {
            associate: function(models) {
                Sensor.belongsTo(models.Location, {
                    foreignKey: "location"
                });

                Sensor.belongsTo(models.SensorType, { 
                    foreignKey: "type"
                });
            }
        }
    });

    return Sensor;
};

Answer 1

Use findAll()with include()and sequelize.fn()for COUNT:

Location.findAll({
    attributes: { 
        include: [[Sequelize.fn("COUNT", Sequelize.col("sensors.id")), "sensorCount"]] 
    },
    include: [{
        model: Sensor, attributes: []
    }]
});

Or you may need to add group:

Location.findAll({
    attributes: { 
        include: [[Sequelize.fn("COUNT", Sequelize.col("sensors.id")), "sensorCount"]] 
    },
    include: [{
        model: Sensor, attributes: []
    }],
    group: ['Location.id']
})

Answer 2

Location.findAll({
        attributes: { 
            include: [[Sequelize.fn("COUNT", Sequelize.col("sensors.id")), "sensorCount"]] 
        },
        include: [{
            model: Sensor, attributes: []
        }]
    });

and it works. but when I add the "limit" I got an error: undefined sensors

Answer 3

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