Storing an array of dates in MongoDB - mongodb

Question

For learning purposes, I am building an app with basic functionality. This is the first time I am using MongoDB and I am wondering whether my data model makes sense or whether I should model it differently.
Basically, this is what should happen:
I have user accounts, they can create "tasks" and execute them. Each time they execute a task, the timestamp should be logged. They can then view a log (journal) which shows all the dates at which they executed a particular task.
My data model looks like this. Does this make sense?
I am especially wondering about the array of dates - is this the right way to go? (the log-Array might become quite long)
{
_id: "51d951922cf9f30200000004",
user: "jon doe",
password: "xxxxxxxxxx",
tasks: [
{
name: "one task",
log: [
ISODate("2010-10-10T20:55:36Z"),
ISODate("2011-10-10T20:55:36Z"),
ISODate("2012-10-10T20:55:36Z")
]
},
{
name: "another task",
log: [
ISODate("2010-10-10T20:55:36Z"),
ISODate("2011-10-10T20:55:36Z"),
ISODate("2012-10-10T20:55:36Z")
]
},
{
name: "one last task",
log: [
ISODate("2010-10-10T20:55:36Z"),
ISODate("2011-10-10T20:55:36Z"),
ISODate("2012-10-10T20:55:36Z")
]
}
]
}

Answer 1

What you have is probably fine. As you grow the sizes of the arrays you might run into some delays in copying large arrays, but there isn't really a space-saving alternative for the logs. The only thing I can think of is a nested document. That will probably update slightly faster once the size is huge, but it will take up more space and won't be nearly as nice or as readable. Rather than having an array with the logs, you would have a document like
{ 0: ISODate("2010-10-10T20:55:36Z" ,
1: ISODate("2010-10-10T20:55:36Z" ,
2: ISODate("2010-10-10T20:55:36Z" }
etc. This will update faster than creating a whole new (larger) array when a log is added, but also take up more space.
If it helps, MongoDB has a page on data modeling with some links you might find useful. http://docs.mongodb.org/manual/core/data-modeling/