Support "count" in queries about sqlprovider HOT 6 CLOSED

I only presently support select, for, join, distinct, where, take, exactlyOne, sortBy, sortByDescending, thenBy, thenByDescending. There are a boat load more keywords not currently supported. (see http://msdn.microsoft.com/en-us/library/hh225374.aspx)

Count is not the same as Seq.length. It has to be formed as part of the various abstract query representations and built intelligently into the SQL query, eg SELECT COUNT(*) FROM Student. This would probably be done if and when I am brave enough to tackle GroupJoin (unless someone feels the urge to do it for me :) )

from sqlprovider.

Yes I know this and tried to implement it. I failed.

I think count is one of the most important operators at this stage since it's good for sanity checks.
It would be awesome if you could add it.
Maybe I can add similar operators by analyzing your commit.

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I'll take a look. I naively assumed it was a matter of renaming Length to Count.

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Count is an odd one because it fires after the query has been generated but before it has been executed, so looking at how this is implemented once it is done might not be that helpful in working out the others.

In fact, it might require some interesting changes to get this to work. I see your point about it being used as a sanity checking tool. I could try to implement this with a priority if it looks like it's going to take you too long to figure out Jack, please do feel free to have a go though but you are going down the rabbit hole with this one ! :)

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ok this is done now - you were close. Except the count happens after the query has been built (it fires the execute method). The transformed projection tree then needs throwing away to be replaced by an execute scalar call, so the way the query is executed has to change.

Note: for some really crazy reason, if you have a select many followed by just a count like this

for x in y
for z in x
count

the count part simply does not fire. Execute does not get triggered, neither is there any indication count has been used in the expression tree. Perhaps one for fsbugs. Putting a select in there will fix it.

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works like a charme. http://forki.github.io/DynamicsNAVProvider/queries.html
Thanks

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