linq - F# Query Expression using join & groupBy in same query -


i decided learn how use query expressions in f# , found the official microsoft documentation. caveats don't seem spelled out i'm sure i've hit problem simple fix don't know why i'm getting error shows.

my thought write query did both join , grouping in same go. example, using sample 'mydatabase' thought try find number of classes each student enrolled in. after writing following query, compiler flags no warning, when go run it gives error.

my query expression:

query {     student in db.student     join course in db.courseselection         on (student.studentid = course.studentid)      groupby student group      select (group.key, group.count())  }  |> seq.iter (fun (student, classcount) -> printfn "student %s has %i classes" student.name classcount)

the error: 

system.invalidoperationexception: not format node 'new' execution sql.    @ system.data.linq.sqlclient.sqlformatter.visitor.visitnew(sqlnew sox)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node) >    @ system.data.linq.sqlclient.sqlformatter.visitor.visitalias(sqlalias alias)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlformatter.visitor.visitselect(sqlselect ss)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlformatter.visitor.visitscalarsubselect(sqlsubselect ss)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlformatter.visitor.visitrow(sqlrow row)    @ system.data.linq.sqlclient.sqlformatter.visitor.visitselect(sqlselect ss)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlformatter.visitor.format(sqlnode node, boolean isdebug)    @ system.data.linq.sqlclient.sqlformatter.format(sqlnode node)    @ system.data.linq.sqlclient.sqlprovider.buildquery(resultshape resultshape, type resulttype, sqlnode node, readonlycollection`1 parentparameters, sqlnodeannotations annotations)    @ system.data.linq.sqlclient.sqlprovider.buildquery(expression query, sqlnodeannotations annotations)    @ system.data.linq.sqlclient.sqlprovider.system.data.linq.provider.iprovider.execute(expression query)    @ system.data.linq.dataquery`1.system.collections.generic.ienumerable<t>.getenumerator()    @ system.linq.enumerable.whereselectenumerableiterator`2.movenext()    @ microsoft.fsharp.collections.seqmodule.iterate[t](fsharpfunc`2 action, ienumerable`1 source)    @ <startupcode$fsi_0008>.$fsi_0008.main@() in c:\users\jdks\library\query expressions.fsx:line 129 stopped due error

i thought out of issue using subquery:

query {     student in db.student     join course in db.courseselection         on (student.studentid = course.studentid)      let count = query {         s in student.name         select course.courseid         count     }      select (student.name, count)  }  |> seq.iter (fun (student, classcount) -> printfn "student %s has %i classes" student classcount)

but gave larger error:

> system.notsupportedexception: sequence operators not supported type 'system.string'.    @ system.data.linq.sqlclient.sqlbinder.visitor.converttofetchedsequence(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitalias(sqlalias a)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlvisitor.visitsource(sqlsource source)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitselect(sqlselect select)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitalias(sqlalias a)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlvisitor.visitsource(sqlsource source)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitselect(sqlselect select)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitalias(sqlalias a)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlvisitor.visitsource(sqlsource source)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitselect(sqlselect select)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlvisitor.visitsequence(sqlselect sel)    @ system.data.linq.sqlclient.sqlvisitor.visitscalarsubselect(sqlsubselect ss)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitsubselect(sqlsubselect ss)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitexpression(sqlexpression expr)    @ system.data.linq.sqlclient.sqlbinder.visitor.fetchexpression(sqlexpression expr)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitnew(sqlnew sox)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitexpression(sqlexpression expr)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitselect(sqlselect select)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitalias(sqlalias a)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlvisitor.visitsource(sqlsource source)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitselect(sqlselect select)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.visitor.visitincludescope(sqlincludescope scope)    @ system.data.linq.sqlclient.sqlvisitor.visit(sqlnode node)    @ system.data.linq.sqlclient.sqlbinder.bind(sqlnode node)    @ system.data.linq.sqlclient.sqlprovider.buildquery(resultshape resultshape, type resulttype, sqlnode node, readonlycollection`1 parentparameters, sqlnodeannotations annotations)    @ system.data.linq.sqlclient.sqlprovider.buildquery(expression query, sqlnodeannotations annotations)    @ system.data.linq.sqlclient.sqlprovider.system.data.linq.provider.iprovider.execute(expression query)    @ system.data.linq.dataquery`1.system.collections.generic.ienumerable<t>.getenumerator()    @ system.linq.enumerable.whereselectenumerableiterator`2.movenext()    @ microsoft.fsharp.collections.seqmodule.iterate[t](fsharpfunc`2 action, ienumerable`1 source)    @ <startupcode$fsi_0015>.$fsi_0015.main@() in c:\users\jdks\library\query expressions.fsx:line 144 stopped due error

my guess don't understand what's going on under hood enough work out error or lead myself solution. possible query want here? there workaround?

when tried running locally got exception

system.exception: grouping on multiple tables not supported yet

i not sure why getting less pretty version of error. if pull groupby out of query, things seem work fine.

query {     student in db.student     join course in db.courseselection         on (student.studentid = course.studentid)     select (student.name, course.id) }  |> seq.countby snd |> seq.iter (fun (student, classcount) -> printfn "student %s has %i classes" student classcount)

Comments

Post a Comment

Popular posts from this blog

node.js - Node js - Trying to send POST request, but it is not loading javascript content -

i have been trying send post request website, , has not been loading full site. i guessing problem node js not loading javascript content, executing it. can see javascript in response, though never loads content javascript files producing in html. what mean is, doesn't execute javascript. how make node js code overcome this, , wait the full website load? have tried native code, , "request' module, both producing same errors. if helps, don't need native javascript. modules fine. some code have tried (request module): var options = { method: 'post', uri: 'https://url', formdata: { 'email': 'email', 'prize': '0', 'transactional': 'on' }, headers: { /* 'content-type': 'application/x-www-form-urlencoded' */ // set automatically } }; rp(options) .then(function (body) { console.log(body) }) .catch(function (err) { console.log(err) }); when fetch content...
Read more

javascript - Replicate keyboard event with html button -

i have tried few ways make happen. have javascript pinball game uses keyboard keys controls. converting application touch screen display. workaround, hoping overlay buttons when clicked simulate keyboard strokes. have done research , sounds should work. using jquery v3.2.1 here things have tried far... html element: <input type="button" class="coil"></input> $('.coil').trigger({type: 'keydown', which: 40, keycode: 40}); with this, not errors, nothing happens. var coilkey = $('body').keydown(function(e) { switch (e.keycode) { case 40: break;} }) $('.coil').click(coilkey); this 1 returns error in console... ((jquery.event.special[handleobj.origtype] || (intermediate value)).handle || handleobj.handler).apply not function below javascript game engine handles key listeners... addkeylistener: function (keyandlistener) { this.keylisteners.push(keyandlistener); }, // gi...
Read more

javascript - Web audio api 5.1 surround example not working in firefox -

i've been playing lott lately web audio api on both firefox , chrome. few days ago started experiment surround set. when trying surround audio in web audio api came notice example works fine in chrome v59 not in firefox v54. // create web audio api context var audioctx = new (window.audiocontext || window.webkitaudiocontext)(); audioctx.destination.channelinterpretation = 'discrete'; audioctx.destination.channelcountmode = 'explicit'; audioctx.destination.channelcount = 6; var oscillators = []; var merger = audioctx.createchannelmerger(6); console.log(audioctx.destination, merger); //merger.channelinterpretation = 'discrete'; //merger.channelcountmode = 'explicit'; //merger.channelcount = 6; var addoscilator = function(channel, frequency) { var oscillator = audioctx.createoscillator(); oscillator.frequency.value = frequency; // value in hertz oscillator.connect(merger,0,channel); oscillator.start(); oscillators.push(o...
Read more