Reputation: 326
MongoDB 'unwind' nested objects
I have a collection in which each document looks something like this:
{
_id: 'dev_id:datetime_hour',
data: {
0: {
0: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
1: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
2: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
59: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}
},
1: {
0: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
1: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
2: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
59: {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}
}
}
I've simplified it here but the fundamental idea is: sensor data is stored every second but is bundled together by the hour. The 'data' field indexes these by the minute and each minute indexes by the second. Therefore a full hours worth of data would yeild 3600 entries in the nested data field. For example to get the sensor data for the first minute and third second I could access the object directly: data.1.3.
This type of schema was recommended for storing time series data by MongoDB.
Stage 1 of my aggregation pipeline looks like this:
db.raw_electric.aggregate(
[
// Stage 1
{
$match: {
_id: { $regex: /^r10a:/ },
datehour: {$gte: ISODate("2016-09-21T17:00:00"), $lte: ISODate("2016-09-21T19:00:00")}
}
}
]
);
Is it possible to 'unwind' the document - similar to how you'd unwind an array so that I can expose each of the nested layers of an object?
Upvotes: 2
Views: 2051
Answers (2)
Reputation: 507
Seems like you have multiple nested objects. In your case if you consider the total arrays that will be unwinded to get 1 hour data, it will be : 1*60*60 = 3600.
Also, multiple nesting unnecessarily adds to the complexity in retrieving and updating data.
You need a more flat structure, which can be attained as follows :-
Create separate document for each minute. The structure would something be like -
{
_id: ObjectId('');
hour: 1,
minute: 1
seconds: [
{
item: 0,
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
{
item: 1,
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}
]
},
{
_id: ObjectId('');
hour: 1,
minute: 2
seconds: [
{
item: 0,
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
},
{
item: 1,
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}
]
}
This structure might subsequently increase the number of documents. But will reduce the complexity involved in querying. Also, with efficient indexing the performance can be maintained. (For large data, you should also look into sharding).
Upvotes: 0
Reputation: 2922
You should have created you schema in following way:
{
_id: 'dev_id:datetime_hour',
data: [{
name: '0',
info: [{}]
}]
}
i.e.your data should be an array of objects.and from that array you can fetch any object using its index.
{
_id: 'dev_id:datetime_hour',
data: [{
name: '0',
info: [{
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}, {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}, {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}, {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}],
{
name: '1',
info: [{
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}, {
voltage_a: float,
voltage_b: float,
voltage_c: float,
current_a: float,
current_b: float,
current_c: float,
current_n: float,
active_power_a: float,
active_power_b: float,
active_power_c: float,
total_active_power: float
}
}]
}
}]
}
Upvotes: 2
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