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Type:
Question
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Resolution: Duplicate
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Priority:
Unknown
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None
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Affects Version/s: None
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Component/s: None
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None
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Dotnet Drivers
You might recognized that the filters
{
potentiallyMissingField: null
}
and
{
$expr: {
$eq: ['$potentiallyMissingField', null]
}
}
do not return the same results when the field is not existent. Whereas the first filter returns all documents where the field is missing or has the null value, the second only returns the documents where the field is existent and null. Negated operators accordingly.
The same is true if you use expressions in projections.
If you use `IgnoreIfNullConvention` like we do, you might have a hard time to express the things with C# Driver because C# does not know undefined.
While in filters you might use the Exists check as well, in projections or Linq it is not as easy.
Consider the projection
myCollection .Aggregate() .Project(x => new MyResultDocument { CountNonNullItems = x.Items.Count(x => x != null), IsRemoved = x.RemovedAt.HasValue, });
you will get a $project stage
{
countNonNullItems: {
$sum: {
$map: {
input: '$items',
in: {
$cond: {
if: {
$ne: ['$$this', null]
},
then: 1,
else: 0
}
}
}
}
},
isRemoved: {
$ne: ['$removedAt', null]
}
}
Which is not what you expect when writing the c# syntax.
Currently we end up with weird expressions like
myCollection .Aggregate() .Project(x => new MyResultDocument { CountNonNullItems = x.Items.Count(x => (x ?? null) != null), IsRemoved = (x.RemovedAt ?? null) != null, });
which will add a
{ $ifNull: ['$removedAt', null] }
Is there a way to handle == null with $lte and != null with $gt (because this is what gives you the expected results) if IgnoreIfNullConvention is used?
- duplicates
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CSHARP-4858 Provide a way to test if a field exists or is missing in a LINQ query
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- Closed
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