Sequelize use upsert function with custom where clause - node.js

Question

I use Sequelize to communicate with my postgres database. I want to use the upsert functionality, but with custom where clause. For example I have this model for volunteers location
module.exports = function (sequelize, DataTypes) {
var volunteer_location = sequelize.define('volunteer_location', {
id: {
type: Sequelize.INTEGER,
allowNull: false,
autoIncrement: true,
primaryKey: true
},
deviceId: {
allowNull: false,
type: Sequelize.STRING
},
latitude: {
allowNull: false,
type: Sequelize.DECIMAL(18, 14)
},
longitude: {
allowNull: false,
type: Sequelize.DECIMAL(18, 14)
},
city: {
allowNull: false,
type: Sequelize.STRING(90)
},
state: {
type: Sequelize.STRING(90)
},
postalCode: {
type: Sequelize.STRING(16)
},
country: {
allowNull: false,
type: Sequelize.STRING(70)
}
}, {
instanceMethods: {
insertOrUpdate: function (requestBody, res) {
volunteer_location.upsert(requestBody).then(function () {
res.sendStatus(200);
});
}
}
});
return volunteer_location;
};
In the insertOrUpdate method I try to use the upsert by giving a json like
location = {
deviceId: req.body.deviceId,
latitude: req.body.latitude,
longitude: req.body.longitude,
city: req.body.city,
state: req.body.state,
postalCode: req.body.postalCode,
country: req.body.country,
volunteer: req.decoded.id
};
where volunteer is a foreign key from table users.
Now the executing says:
CREATE OR REPLACE FUNCTION pg_temp.sequelize_upsert() RETURNS integer
AS $func$ BEGIN INSERT INTO "volunteer_locations" some values RETURN
1; EXCEPTION WHEN unique_violation THEN UPDATE "volunteer_locations"
SET some values WHERE (("id" IS NULL AND "volunteer" = 1));
RETURN 2; END; $func$ LANGUAGE plpgsql; SELECT * FROM
pg_temp.sequelize_upsert();
id and volunteer is a set of primary keys. I want to change the WHERE clause on the UPDATE by checking only the volunteer value, because I don't know the value of the id.
Is this possible? Or I have to use
findOne(...).then(function () {
//update
});
EDIT
I set volunteer with the attribute unique: true and it replaced the where clause with WHERE (("id" IS NULL AND "volunteer" = 1) OR "volunteer" = 1);, which means that the update works. But I don't know if this is very efficient. If anyone knows a better solution please let me know.