MongoDB push to null array

Question

So today I realized I have a problem with updating/pushing to an array. I have an array in a class that is just a auto property

public List<things> Things { get; set; }

This can get put in the database as null and if I later on need to write a query like

var query = Query.EQ("_id", something.Id);
var update = Update.Push("Things", thing.ToBsonDocument());

coll.Update(query, update);

I now have a problem because my update will throw an exception that I tried to push to a NULL array.

I solved this by just putting a private backer on the class

private List<things> _things = new List<things>();
public List<things> Things { get { return _things;} set { _things = value;} }

Now at least a new instance will have an empty array and someone would need to explicitly say

Things = null

But I was wondering is there a better way to solve this. Decorators? Mongo Index? something to say hey this field must ALWAYS be an array.

I've always been kind of dubious of auto properties and prefer using the private backer especially for non primitives. Just wondering if a more robust solutions exist that's built into the Mongo engine.

MarkKGreenway · Accepted Answer · 2014-07-29 20:23:36Z

3

If you would prefer to use autoproperties you can simply have the constructor create the empty list.

public YourClass() 
{
   Things = new List<things>();
}

Then the auto property works simply and the only spot with any ugliness is the constructor.

This is What I do

answered Jul 29, 2014 at 20:23

MarkKGreenway

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Václav Mikeska · Accepted Answer · 2016-06-14 16:21:32Z

2

Also some convert script when you are starting your application is not a bad idea

<code>
var emptyInterUsers = db.List<UserEntity>(u => u.Interests == null);
if (emptyInterUsers.Any())
{
    foreach (var u in emptyInterUsers)
    {
        if (u.Interests == null)
        {
            var filter = db.F<UserEntity>().Eq(f => f.id, u.id);
            var update = db.U<UserEntity>().Set(f => f.Interests, new List<int>());
            var res = await db.UpdateAsync(filter, update);
        }
    }                   
}
</code>

answered Jun 14, 2016 at 16:21

Václav Mikeska

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