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<div class=Section1>
<p class=MsoNormal><span style='color:#1F497D'>I would like to divide this and
answer in two parts.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Part with Parameters direction
is something we need. As it is already written , mostly to be able to execute and
get results from stored procedures.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>About executing SQL statements
and trying to squeeze result of it inside FDO class/schema, I think it is too complex
and in my mind without chance to be successful. There is so many cases in which
it can't be done properly. If we are missing some info about result of
execution of SQL we could look into existing specs like ODBC and add those. I
agree FDO application should be able to get all necessary info about executed
SQL so app can be written in generic way but I don't see putting that info in FDO
class or reengineering sql etc.. I believe what can be done with api's like odbc
is ok for fdo api too.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Haris<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
fdo-internals-bounces@lists.osgeo.org
[mailto:fdo-internals-bounces@lists.osgeo.org] <b>On Behalf Of </b>Orest
Halustchak<br>
<b>Sent:</b> Wednesday, June 03, 2009 3:28 PM<br>
<b>To:</b> FDO Internals Mail List<br>
<b>Subject:</b> [fdo-internals] Use of SQL pass through<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Hi,<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I would like to solicit feedback, discussion, and
suggestions on requirements and issues that we are seeing with the
FdoISQLCommand which is used for the purpose of SQL pass through for some of
the RDBMS-based providers.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Please see the discussion below.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks,<o:p></o:p></p>
<p class=MsoNormal>Orest.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal style='mso-margin-top-alt:1.8pt;margin-right:12.0pt;
margin-bottom:0in;margin-left:0in;margin-bottom:.0001pt'><b><span
style='font-size:14.5pt;font-family:"Arial","sans-serif";color:black;
letter-spacing:-.2pt'>Enhanced SQL Command Support Discussion<o:p></o:p></span></b></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span
style='font-size:12.0pt;font-family:"Arial","sans-serif";color:black;
letter-spacing:-.2pt'>Overview<o:p></o:p></span></b></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>The FDO
API currently defines support for a SQL command that allows for pass-through execution
of SQL statements either through a non-query execution of the SQL statement
directly in the underlying Data Store, or through a query mechanism that
returns a simple data reader listing the properties returned as a result of the
SQL execution. The definition of the SQL command has remained fairly static
over the last number of releases as primary development efforts have focused on
extending other aspects of the FDO API, implementing new providers, etc.
However, requirements for change to the SQL command have accumulated for us as
RDBMS providers have implemented SQL pass through support and clients have
attempted to integrate use SQL pass through into their applications in a
seamless manner. While we generally expect applications to be using the generic
FDO Select and other commands using FDO expressions, application still need to
execute direct SQL against RDBMS-based providers on an exception basis for
things that cannot do through FDO. While we hope to improve the FDO expression
capabilities over time, there will always be this need for direct SQL
processing for exception cases.<o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>This
email is meant to start discussion on how to handle the requirements that
we’ve been seeing and to get feedback on how to modify the FDO api to
handle these requirements. We have some ideas as described below, but would
like to get other feedback. We’ll draft an RFC once we get close to a
consensus on how it should look.<o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span
style='font-family:"Verdana","sans-serif";color:black'>Requirements<o:p></o:p></span></b></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>One key
request has been the desire to have the FDO API support SQL pass-through commands
that return an FDO feature reader, referencing a proper FDO schema, not simply
an FDO data reader. The feature reader will contain proper geometry properties,
relations and associations. This enhancement is also intended to allow client
applications that use FDO Feature Readers to code their applications in a
generic manner so that data coming back from Select or SQL Pass Through
statements can be processed in a uniform manner, thus reducing complexity,
costs and time to implement. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>Other
more SQL specific requirements related to this have also arisen, including: <o:p></o:p></span></p>
<ul type=disc>
<li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l1 level1 lfo3'><span style='font-size:10.0pt;font-family:
"Verdana","sans-serif"'>A need to allow a client to set the size of the
fetch array an FDO provider will use when executing SQL statements ([OH] I
still have an issue with this one. Fetch sizes are internal tuning parameters
and are not FDO api concepts. Other providers that deal with select or
insert buffering have default internal sizes.)<o:p></o:p></span></li>
<li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l1 level1 lfo3'><span style='font-size:10.0pt;font-family:
"Verdana","sans-serif"'>A need to specify bind variables for the SQL
command, including arrays of bind variables. Since SQL commands may
include stored procedure execution, bind variables need indication of
whether they are input, output, or return parameters.<o:p></o:p></span></li>
</ul>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span
style='font-size:12.0pt;font-family:"Arial","sans-serif";color:black;
letter-spacing:-.2pt'>Discussion<o:p></o:p></span></b></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>In
general, the intent of SQL pass-through is to deal with physical schemas. There
is no parsing of the SQL statements, and what are identified are physical
schema tables, columns, functions, commands, etc. The SQL statement can be any
SQL command, not just select, but any DML (select, insert, update, delete) or
any DDL (create, drop, alter, …). However, FDO feature readers deal with
FDO logical schemas, which is at a different conceptual level. It’s the
mixing of these levels that causes difficulty for applications using the FDO
API. Applications are required to use different code pathways to handle select
statement as opposed to direct SQL execution. If clients could use the result
of either of these types of operations in a generic routine or component, such
as a Data Table or Symbolization packages, applications would be provided a
much more seamless and dynamic mechanism on which they can build and extend
their applications. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>To a
certain degree, the current FDO feature reader implementation assumes an FDO
class definition is directly related to the properties being returned. With
physical schema SQL (let’s say just Select command), there isn’t
necessarily any FDO class definition that applies. This is why currently the
SQL command's Execute method returns a data reader, which handles any
generically returned data. Note that the FDO select aggregates command
doesn’t return a feature reader either, since it’s returning
computed data. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>One
response to this issue has been to suggest that providers reverse engineer the
select results and attempt to find the FDO class definition (coming from a
describe schema request) that matches it. Other suggestions have been to
construct a class definition on the fly, one that would not result from a call
to describe schema. If the select is from a single table, providers would find
the class definition that is based on that table and use it. However, then matching
up the columns being selected with the properties in the logical schema, there
may be some slight differences. This would result in the mixing of physical
schema and logical schema elements together. For example, class names that are
not the same as table names, property names that are not the same as column
names, the use of additional computed columns, inclusion of pkey columns, etc.
Granted that in many cases, the logical and physical views would be virtually
identical. However, since that cannot be guaranteed, the design that is adopted
will have to be able to handle the general case. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>To
account for these scenarios, providers will need to be modified to reverse
engineer class definitions from the selected data and not attempt to match the
select request to an existing FDO class. In reality, FDO Providers will be
required to handle this in any case since a generic SQL select may not match up
at all with an existing FDO class. An example of this can be found when
selecting from a table with an owner that is different from the connected data
store. For example, Connect to data store called Denver and select from
Boulder.Roads – the schema may or may not be similar to Denver.Roads. In
these types of circumstances, providers should manufacture a new class
definition. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>In
cases where the resulting columns come from an existing FDO feature table, a
provider can return the class definition corresponding to that table. In cases
where the columns come from an unknown table, a class definition can be
constructed on the fly. By definition, the FDO class definition returned by a
feature reader does not necessarily correspond exactly to an existing FDO class
definition. Existing class definitions may contain the properties that were
asked for in the Select command, plus additional computed properties. It is
perfectly legal to return a constructed class definition, which is only valid
for the select that was executed, and not usable for further updates or
inserts. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>In the
circumstance that a computed class is generated, the FDO class
definition’s IsComputed property will return true. In this manner,
applications are able to distinguish the content of the feature reader
responses coming from the providers and tailor their implementation
accordingly. In such a situation, some care will also need to be given to the
name of the generated FDO schema and class definitions. At this point no
standards exist for naming auto-generated schema, class and property names. It
would be beneficial if, as a result of this RFC, some uniform naming
conventions could be adopted. <o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>Providers
that do return feature readers from SQL commands will need to come up with the
appropriate class definition that the feature reader could expose. Here are a
few general use cases: <o:p></o:p></span></p>
<ul type=disc>
<li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l0 level1 lfo6'><span style='font-size:10.0pt;font-family:
"Verdana","sans-serif"'>Select is against a table that has an existing
class definition and the select returns the same information as defined by
the class definition (e.g. select * from roads). <o:p></o:p></span></li>
<li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l0 level1 lfo6'><span style='font-size:10.0pt;font-family:
"Verdana","sans-serif"'>Select is against a table that has an existing class
definition, but the select returns other information such as a subset of
properties or additional computed properties. The FDO select command
handles this type of case as well. The class definition returned by the
feature reader includes the specific properties for that select. <o:p></o:p></span></li>
<li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l0 level1 lfo6'><span style='font-size:10.0pt;font-family:
"Verdana","sans-serif"'>Select is against a table that doesn’t have
an existing class definition. Providers will be required to generate a
temporary class definition. <o:p></o:p></span></li>
<li class=MsoNormal style='color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l0 level1 lfo6'><span style='font-size:10.0pt;font-family:
"Verdana","sans-serif"'>Select is against a table that has an existing
class definition, but the select is an aggregation that doesn’t
return actual objects (e.g. select count(*), max(length) from roads). In
this case it doesn’t make sense for the provider to return the same
class name as for the underlying table since it is not actually returning
road objects at all. This is basically another temporary class definition.<o:p></o:p></span></li>
</ul>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span
style='font-family:"Arial","sans-serif";color:black;letter-spacing:-.2pt'>FDO
API Ideas</span></b><b><span style='font-size:10.5pt;font-family:"Arial","sans-serif";
color:black;letter-spacing:-.2pt'><o:p></o:p></span></b></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>In
order to support the SQL pass-through objective outlined above, the FDO API
will need to be modified to provide a new capability function to state that this
is supported, and to provide a way to return an explicit FDO Feature Reader.
Two possibilities have been identified for returning the feature reader. One
idea is to add a new ExecuteFeatureReader (or similar name) method to
FdoISQLCommand. The existing ExecuteReader method will remain as is for
backwards compatibility. Another possibility is to keep the SQL pass through
interface unchanged but provide a utility that will convert the returned SQL
Data Reader into a Feature Reader after the fact.<o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>A related
question is around the class definition that would be generated from the SQL
since it often would be a temporary class definition for the command and not
something found from the FDO Describe Schema command. The feature reader would
expose that class definition, but would applications need to get that earlier,
e.g. with a new method on FdoISQLCommand to describe the generated class
definition prior to getting the reader?<o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span
style='font-size:12.0pt;font-family:"Arial","sans-serif";color:black;
letter-spacing:-.2pt'>Parameter Direction<o:p></o:p></span></b></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>FDO
already includes API’s for defining and using parameters (bind
variables). However, there is no indication of direction (input versus output)
and if an application is planning to use stored procedure calls in the SQL pass
through, they would need to provide some indication of input, output, or return
parameters. A possibility is to add a new FdoParameterDirection enumeration and
add set/get methods to the FdoParameterValue or FdoParameterValueCollection
interface.<o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'>A
related question is whether FdoISQLCommand needs the application to tell it
whether the SQL command being executed is a stored procedure call or some other
type of SQL? We want to avoid having providers be forced to parse SQL where
currently they probably all just send the SQL directly to the underlying
server. The ExecuteNonQuery versus ExecuteReader methods that the application
uses already tell the provider whether to expect results back from the SQL or
not. A stored procedure call is a “non-query” but can return
results, so is it another case?<o:p></o:p></span></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Verdana","sans-serif";color:black'><o:p> </o:p></span></p>
<p class=MsoNormal><o:p> </o:p></p>
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