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Eduard Lebedyuk · May 11, 2018

Sessions or No Sessions 

REST mainly disallows sessions as a mechanism of data transfer. Stateless as stated in REST dissertation by Roy Fielding has three aims:

  • visibility
  • reliability
  • scalability

Visibility is improved because a monitoring system does not have to look beyond a single request datum in order to determine the full nature
of the request. In my opinion that's the most important one and it mainly deals with storing session data in between requests.

Let's say you provide a newsfeed API. There's a lot of news so users get them by pages of 10 elements. Clients can access news in two different ways:

  1. http://host/api/news/next - in this case the server remembers last page of news the client requested and returns the next one. That's not stateless.
  2. http://host/api/news/:pagenmumber - in this case client remembers last page of news he requested and asks for the next one by incrementing page number by 1. That's stateless.

Reliability is improved because it eases the task of recovering from partial failures. Where partial failure is defined as (from Waldo J,
Wyant G, Wollrath A, Kendall S. A Note on Distributed Computing.):

Partial failure is a central reality of distributed computing. Both the local and the distributed world contain components that are subject to periodic failure.

In the case of local computing, such failures are either total, affecting all of the entities that are working together in an application, or detectable by some central resource allocator (such as the operating system on the local machine).

This is not the case in distributed computing, where one component (machine, network link) can fail while the others continue. Not only is the failure of the distributed components independent, but there is no common agent that is able to determine what component has failed and inform the other components of that failure, no global state that can be examined that allows determination of exactly what error has occurred.

In a distributed system, the failure of a network link is indistinguishable from the failure of a processor on the other side of that link.

Sessions as an authentication/authorisation mechanism do not affect Reliability.

Scalability is improved because not having to store state between requests allows the server component to quickly free resources, and
further simplifies implementation because the server doesn't have to manage resource usage across requests. Not relevant in our case as Session still gets created, just destroyed immediately after the request is done.


To sum up: REST APIs can use sessions as authentication mechanism, but not as a data transfer mechanism.

Eduard Lebedyuk · May 10, 2018

Maybe remove $zf calls?

Here's sample code:

 ClassMethod Test()
{
//Create new Gateway connection object
set gc=##class(%SQLGatewayConnection).%New()
if gc=$$$NULLOREF quit $$$ERROR($$$GeneralError,"Cannot create %SQLGatewayConnection.")
  
//Make connection to target DSN
set pDSN="Cache Samples"
set usr="_system"
set pwd="SYS"
set sc=gc.Connect(pDSN,usr,pwd,0) 
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
if gc.ConnectionHandle="" W !, $$$ERROR($$$GeneralError,"Connection failed") QUIT
  
set sc=gc.AllocateStatement(.hstmt) 
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
  
//Prepare statement for execution
set pQuery= "select Name, DOB from Sample.Person WHERE Name %STARTSWITH ?"
set sc=gc.Prepare(hstmt,pQuery) 
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
//Bind Parameters
set sc=gc.BindParameter(hstmt,1,1,1,12,30,0,30)
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
set var = "A"
set sc=gc.SetParameter(hstmt,$LB(var),1)
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
//Execute statement
set sc=gc.Execute(hstmt)
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
//Get list of columns returned by query
set sc=gc.DescribeColumns(hstmt, .columnlist) 
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
 
//display column headers delimited by ":"
set numcols=$listlength(columnlist)-1 //get number of columns
for colnum=2:1:numcols+1 {
    Write $listget($listget(columnlist,colnum),1),":"
   }
write !
 
//Return first 20 rows 
set sc=gc.Fetch(hstmt)
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
s rownum=1
while((gc.sqlcode'=100) && (rownum<=20)) {
       for ii=1:1:numcols {
       s sc=gc.GetData(hstmt, ii, 1, .val)
       w " "_val
       if $$$ISERR(sc) break
       }
       s rownum=rownum+1
  write !
  set sc=gc.Fetch(hstmt)
if $$$ISERR(sc) break
   }
    
  //Close cursor and then disconnect
set sc=gc.CloseCursor(hstmt)
if $$$ISERR(sc) w !, $SYSTEM.OBJ.DisplayError(sc) QUIT 0
  
set sc=gc.Disconnect()
  
quit sc
}

Check BindParameter method and EnsSQLTypes for SQL types macro definitions. Varchar maybe.

You can also try to call PutData method and similar methods (by passing parts of stream there).