MongoDB C# Nullable Datetime Query

Question

I'm trying to query a over mongoDB and I get the following error:

Unable to determine the serialization information for the expression: c.IndexMetadata.Indexed.HasValue.

where Indexed is a nullable datetime

my query is the following:

Collection.AsQueryable<Candidate>(c => !c.IndexMetadata.Indexed.HasValue || c.IndexMetadata.Updated.Value > c.IndexMetadata.Indexed.Value).ToList();

both indexed and updated are type of nullable datetime

I guess that's because there's no direct translation from HasValue into a mongo Query, any workaround?

You can't compare two fields with each other. You must compare them with constants unfortunately. A good way to figure out how to write a query is to write it in the shell first and make sure it works as you expect. — Craig Wilson
– Craig Wilson, Commented Apr 19, 2014 at 12:50
@CraigWilson I can refactor to avoid two columns comparison, but I still need to solve the hasValue error, thanks for the heads up! — pedrommuller
– pedrommuller, Commented Apr 19, 2014 at 16:58
Perhaps you can use != null instead for now. File a jira issue at jira.mongodb.com in the C# project. — Craig Wilson
– Craig Wilson, Commented Apr 19, 2014 at 17:13
@CraigWilson the null comparison did the trick thanks for the help! — pedrommuller
– pedrommuller, Commented Apr 19, 2014 at 17:39

2 revs · Accepted Answer · 2014-05-26 21:06:51Z

7

You can compare the DateTime? to null instead of using HasValue:

Collection.AsQueryable<Candidate>(
    c => 
        c.IndexMetadata.Indexed == null || 
        c.IndexMetadata.Updated.Value > c.IndexMetadata.Indexed.Value).
    ToList();

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