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Type:
Improvement
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: Querying
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None
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Query Optimization
With update the positional operator can be combined with additional fields after the dollar sign, for example 'a.$.b' to indicate the 'b' field within the matched array element. This is not yet supported with positional projections.
Observed behavior: Projecting
{ 'a.$.b':1 }is equivalent to projecting
{ 'a.$':1 }.
Expected behavior: Projecting
will project only the 'b' field within the matching array element.
Test
c = db.c;
c.drop();
c.save( { a:[ { b:10, c:1 }, { b:5, c:1 } ] } );
// Update the 'b' field within the matching array element.
c.update( { 'a.b':5 }, { $set:{ 'a.$.b':6 } } );
printjson( c.findOne() );
// Projects the entire matching array element.
printjson( c.find( { 'a.b':6 }, { 'a.$':1 } ).toArray() );
// Projects the entire matching array element (contrary to expected behavior).
printjson( c.find( { 'a.b':6 }, { 'a.$.b':1 } ).toArray() );
// Projects the 'b' fields within all array elements.
printjson( c.find( { 'a.b':6 }, { 'a.b':1 } ).toArray() );
- is related to
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SERVER-6864 positional operator projection inclusion can mess up array based non positional operator
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- Closed
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SERVER-43334 Disallow additional path components after the positional projection ("$") operator
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- Closed
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