C# mongodb - how to update nested array elements

Question

I have the following JSON structure that represents an item

{
    Id: "a",
    Array1: [{
        Id: "b",
        Array2: [{
            Id: "c",
            Array3: [
                {...}
            ]
        }]
    }]
}

I need to be able to either replace the array element in Array2 with a new item or to replace just Array3 with a new array.

Here is my code to replace the array item in Array2:

await Collection.UpdateOneAsync(
    item => item.Id.Equals("a") &&
    item.Array1.Any(a => a.Id.Equals("b")) &&
    item.Array1[-1].Array2.Any(b => b.Id.Equals("c")),
    Builders<Item>.Update.Set(s => s.Array1[-1].Array2[-1], newArray2Item)
);

When executing this code I'm getting this error:

"A write operation resulted in an error.
 Too many positional (i.e. '$') elements found in path 'Array1.$.Array2.$'"

Here is my code to replace Array3 within Array2:

await Collection.UpdateOneAsync(
        item => item.Id.Equals("a") &&
        item.Array1.Any(a => a.Id.Equals("b")) &&
        item.Array1[-1].Array2.Any(b => b.Id.Equals("c")),
        Builders<Item>.Update.Set(s => s.Array1[-1].Array2[-1].Array3, newArray3)
    );

And this is the error:

"A write operation resulted in an error.
 Too many positional (i.e. '$') elements found in path 'Array1.$.Array2.$.Array3'"

I'm using C# MongoDB driver version 2.5.0 and MongoDB version 3.6.1

I found this Jira ticket Positional Operator Matching Nested Arrays that says the problem was fixed and they suggested this syntax for the update

Update all matching documents in nested array:

db.coll.update({}, {$set: {“a.$[i].c.$[j].d”: 2}}, {arrayFilters: [{“i.b”: 0}, {“j.d”: 0}]})
Input: {a: [{b: 0, c: [{d: 0}, {d: 1}]}, {b: 1, c: [{d: 0}, {d: 1}]}]}
Output: {a: [{b: 0, c: [{d: 2}, {d: 1}]}, {b: 1, c: [{d: 0}, {d: 1}]}]}

So I converted it to my elements:

db.getCollection('Items').update(
{"Id": "a"},
{$set: {"Array1.$[i].Array2.$[j].Array3": [newArray3]}}, 
{arrayFilters: 
    [
        {"i.Id": "b"}, 
        {"j.Id": "c"}
    ]}
)

And got this error:

cannot use the part (Array1 of Array.$[i].Array2.$[j].Array3) to traverse the element

Any ideas on how to solve this error?

It's not pretty but as a shortcut you can always just write your updates using strings like you'd write them in the shell and then pass them to the Update() method. — dnickless
– dnickless, Commented Feb 19, 2018 at 14:38
This is why I gave the sample from Jira. It still doesn't work,,, — Liran Friedman
– Liran Friedman, Commented Feb 19, 2018 at 14:41
You will need an updated client for this to work (try the "mongo.exe" shell that came with your distribution): stackoverflow.com/questions/47225822/… — dnickless
– dnickless, Commented Feb 19, 2018 at 15:00
I can't use mongo.exe in C#... the link you sent me is talking about robomongo. — Liran Friedman
– Liran Friedman, Commented Feb 19, 2018 at 15:06
I know. ;) The last query you gave in your example is a string based one that you should be able to run inside mongo.exe without getting an error. That's all I'm saying. Once you've got that query working you can use the filter and update parts of it to create a C# version. — dnickless
– dnickless, Commented Feb 19, 2018 at 15:12

dnickless · Accepted Answer · 2018-02-19 15:23:15Z

8

Here's the C# version of what you need:

var filter = Builders<Item>.Filter.Eq("Id", "a");
var update = Builders<Item>.Update.Set("Array1.$[i].Array2.$[j].Array3", new[] { new Item { Id = "d" } });
var arrayFilters = new List<ArrayFilterDefinition> { new JsonArrayFilterDefinition<Item>("{'i.Id': 'b'}"), new JsonArrayFilterDefinition<Item>("{'j.Id': 'c'}") };
var updateOptions = new UpdateOptions { ArrayFilters = arrayFilters };
collection.UpdateOne(filter, update, updateOptions);

answered Feb 19, 2018 at 15:23

dnickless

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10 Comments

Liran Friedman Over a year ago

It doesn't work from C# but does work from Studio 3T any idea why? It doesn't give an error and looks like the command went through, but the update does not apply...

Liran Friedman Over a year ago

The only difference I see is that I use the filters for the id like this: "_id", "ObjectId(ITEM_ID)" and like this: "{\"i._id\": ObjectId(ARRAY_ITEM_ID)}" because the id's are generated by mongo and represented by ObjectId. Any suggenstions?

dnickless Over a year ago

I would suggest you log your queries (db.setProfilingLevel(2)) and check the MongoDB log file for what the resulting query looks like when you run your C# code. That alone is likely to reveal the problem, I guess. Otherwise you could run that resulting query in Studio3T and see if it produces the right result there (it won't) and why it does not.

dnickless Over a year ago

mkyong.com/mongodb/mongodb-where-is-the-log-file description for Linux but also pretty much applicable for Windows.

Liran Friedman Over a year ago

I found some log file under C:\data\log\mongod.log, but it doesn't write anything to it... I couldn't find anything that looks like /var/log/mongodb/mongodb.log

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