Details
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Type:
Bug
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Status: Open
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Priority:
Major - P3
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Affects Version/s: 2.11.0
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Fix Version/s: None
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Component/s: Builders
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Labels:None
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Environment:I've verified this behaviour both on Windows as well as in a Linux container
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Case:
Description
I believe I’ve found a bug related to projection, specifically when you map an array that is a deep descendant of the document root.
Suppose this is my model:
public class DummyContainer |
{
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public DummyContainer(IList<Dummy> dummies) |
{
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|
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Dummies = dummies;
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this.Id = ObjectId.GenerateNewId().ToString(); |
}
|
|
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public string Id { get; private set; } |
public IList<Dummy> Dummies { get; private set; } |
}
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public class Dummy |
{
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public Dummy(string name) |
{
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this.Name = name; |
this.Id = ObjectId.GenerateNewId().ToString(); |
}
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|
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public string Id { get; private set; } |
public string Name { get; private set; } |
}
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First, an example that works:
Let’s say I insert one document of type DummyContainer into an empty collection:
collection.InsertOneAsync(new DummyContainer(new[] |
{
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new Dummy("SomeValue1"), |
new Dummy("SomeValue2"), |
}));
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And then I load all documents from that collection, projected into this type:
class DummyContainerWithDummyNames |
{
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public string ContainerId { get; set; } |
public IEnumerable<string> DummyNames { get; set; } |
}
|
Here we go:
var dummyNamesByUsingFindAsync = await (await collection.FindAsync(Builders<DummyContainer>.Filter.Empty, new FindOptions<DummyContainer, DummyContainerWithDummyNames> { |
Projection = Builders<DummyContainer>.Projection.Expression(x => new DummyContainerWithDummyNames |
{
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ContainerId = x.Id,
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DummyNames = x.Dummies.Select(d => d.Name)
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})
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})).ToListAsync();
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var dummyNamesUsingQuery = await collection.AsQueryable()
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.Select(x => new DummyContainerWithDummyNames |
{
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ContainerId = x.Id,
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DummyNames = x.Dummies.Select(d => d.Name)
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})
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.ToListAsync();
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Result:
Both dummyNamesByUsingFindAsync and dummyNamesUsingQuery contain one document, and in both cases the property DummyNames is populated with ["SomeValue1", "SomeValue2"].
An example that shows the bug:
Ok, in order to reproduce the bug, we’re gonna wrap the DummyContainer in a DummyContainerWrapper and let this be our root entity:
public class DummyContainerWrapper |
{
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public DummyContainerWrapper(DummyContainer container) |
{
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Container = container;
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this.Id = ObjectId.GenerateNewId().ToString(); |
}
|
|
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public string Id { get; private set; } |
public DummyContainer Container { get; private set; } |
}
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We’re gonna insert such a document to a new collection:
await collection.InsertOneAsync(new DummyContainerWrapper(new DummyContainer(new[] |
{
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new Dummy("SomeValue1"), |
new Dummy("SomeValue2"), |
})));
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And just like before, we’re gonna query the collection for all documents and project them into the same type we used above:
var dummyNamesByUsingFindAsync = await (await collection.FindAsync(Builders<DummyContainerWrapper>.Filter.Empty, new FindOptions<DummyContainerWrapper, DummyContainerWithDummyNames> { |
Projection = Builders<DummyContainerWrapper>.Projection.Expression(x => new DummyContainerWithDummyNames |
{
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ContainerId = x.Id,
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DummyNames = x.Container.Dummies.Select(d => d.Name)
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})
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})).ToListAsync();
|
|
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var dummyNamesUsingQuery = await collection.AsQueryable()
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.Select(x => new DummyContainerWithDummyNames |
{
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ContainerId = x.Id,
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DummyNames = x.Container.Dummies.Select(d => d.Name)
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})
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.ToListAsync();
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And this is where we see the bug:
dummyNamesUsingQuery has one element, who’s DummyNames }}property is an {{IEnumerable<string> (the concrete type is List<string>) populated with{{ ["SomeValue1", "SomeValue2"]}}.
dummyNamesByUsingFindAsync }}on the other hand also has one element, but it´s {{DummyNames }}property is of type {{System.Linq.Enumerable.SelectListIterator<MyTestProgram.Dummy, string>, and the values are both null.