使用linq计算特定条件下的记录数

Question

I'm trying to retrieve some information form a table as follow:

//Fish table: fishid(int32), SpeciesName(nvarchar(50)),age(int?), weight(int?)   

 (from f in Fish 
  where f.SpeciesName=="COD" || f.SpeciesName=="Salmon"
  select f
 ).GroupBy(g=>g.SpeciesName)
  .Select(s= > new 
   { 
      Species=s.Key, 
      Age= (from age_count in Fish where age_count.SpeciesName== s.key && age_count.age!=null  select age_count).Count(),
      Weight= (from Weight_count in Fish where Weight_count.SpeciesName== s.key && Weight_count.Weight!=null  select weight_count).Count()
   };

Now, while this is working, i'm thinking there must be a better way of doing it. Can someone suggest some better code?

Thanks

Answer 1

This should do the same:

var result = Fish.Where(f => f.SpeciesName == "COD" || f.SpeciesName == "Salmon")
                 .GroupBy(f => f.SpeciesName)
                 .Select(g => new {
                    Species = g.Key,
                    Age = g.Count(f => f.Age != null),
                    Weight= g.Count(f => f.Weight != null),
                  });

The Age and Weight aggregations seem a little uncanny - they are counting the number of records in each group where the associated property is not null. Was this your intention, or were you after something like an "Average Age" of fish in each group?