2011-06-29
2011-06-29. Open Source › mORMot Framework
Our ORM framework has been released as version 1.14.
It's mainly a bug-fix release:
2011-06-16
2011-06-16. Pascal Programming
After a question on StackOverflow, I wanted to comment about the speed of generated code by diverse Delphi compiler versions.
Since performance matters when we write general purpose libraries like ours, we have some feedback to propose:
2011-06-07
2011-06-07. Pascal Programming
In order to let our TSynLog logging class intercept all
exceptions, we use the low-level global RtlUnwindProc pointer,
defined in System.pas.
Alas, under Delphi 5, this global RtlUnwindProc variable is not
existing. The code calls directly the RtlUnWind Windows API
function, with no hope of custom interception.
Two solutions could be envisaged:
Sytem.pas source code, adding the new
RtlUnwindProc variable, just like Delphi 7; The first solution is simple. Even if compiling System.pas is a
bit more difficult than compiling other units, we already made that for our
Enhanced
RTL units. But you'll have to change the whole build chain in order to
use your custom System.dcu instead of the default one. And some
third-party units (only available in .dcu form) may not like the
fast that the System.pas interface changed...
So we used the second solution: change the assembler code in the running
process memory, to let call our RtlUnwindProc variable instead of
the Windows API.
2011-06-07. Pascal Programming
For our ORM, we needed a class variable to be available for each
TSQLRecord class type.
This variable is used to store the properties of this class type, i.e. the
database Table properties (e.g. table and column names and types) associated
with a particular TSQLRecord class, from which all our ORM objects
inherit.
The class var statement was not enough for us:
- It's not available on earlier Delphi versions, and we try to have our
framework work with Delphi 6-7 up to XE;
- This class var instance will be shared by all classes inheriting
from the class where it is defined - and we need ONE instance PER class type,
not ONE instance for ALL
We needed to find another way to implement this class variable.
An unused VMT slot in the class type description was identified, then each class definition was patched in the process memory to contain our class variable.
2011-06-06
2011-06-06. Open Source › Synopse PDF engine
Our SynPdf unit has been refreshed to the 1.13 version.
2011-06-05
2011-06-05. Open Source › mORMot Framework
This is a major step for the framework.
Among a lot of new features and bug fixes:
TDynArray
wrapper);TSQLRecordRTree to implement R-Tree
virtual tables;Open Source project, for Delphi 6 up to XE, licensed under a MPL/LGPL/GPL tri-license.
2011-06-02
2011-06-02. Open Source › mORMot Framework
The SQLite3 engine defines some standard SQL functions, like
abs() min() max() or upper().
A complete list is available at http://www.sqlite.org/lang_corefunc.html
One of the greatest SQLite3 feature is the ability to define custom SQL functions in high-level language. In fact, its C API allows to implement new functions which may be called within a SQL query. In other database engine, such functions are usually named UDF (for User Defined Functions).
Our framework allows you to add easily such custom functions, directly from Delphi classes.
2011-06-02. Open Source › mORMot Framework
When it deals with parsing some (textual) content, two directions are
usually envisaged. In the XML world, you have usually to make a choice
between:
- A DOM parser, which creates an in-memory tree structure of objects mapping
the XML nodes;
- A SAX parser, which reads the XML content, then call pre-defined
events for each XML content element.
In fact, DOM parsers use internally a SAX parser to read the XML content. Therefore, with the overhead of object creation and their property initialization, DOM parsers are typically three to five times slower than SAX. But, DOM parsers are much more powerful for handling the data: as soon as it's mapped in native objects, code can access with no time to any given node, whereas a SAX-based access will have to read again the whole XML content.
Most JSON parser available in Delphi use a DOM-like approach. For instance, the DBXJSON unit included since Delphi 2010 or the SuperObject or DWS libraries create a class instance mapping each JSON node.
In a JSON-based Client-Server ORM like ours, profiling shows that a lot of time is spent in JSON parsing, on both Client and Server side. Therefore, we tried to optimize this part of the library.
2011-06-02. Open Source › mORMot Framework
When use the so-called BATCH sequences?
In a standard Client-Server architecture, especially with the common
understanding (and most implementations) of a RESTful service, any Add /
Update / Delete method call requires a back and forth flow to then from
the remote server.
In case of a remote connection via the Internet (or a slow network), you could have some 100 ms of latency: it's just the "ping" timing, i.e. the time spent for your IP packet to go to the server, then back to you.
If you are making a number of such calls (e.g. add 1000 records), you'll have 100*1000 ms = 100 s = 1:40 min just because of this network latency!
The BATCH sequence allows you to regroup those statements into just ONE remote call. Internally, it builds a JSON stream, then post this stream at once to the server. Then the server answers at once, after having performed all the modifications.
2011-06-02. Open Source › mORMot Framework
An R-Tree is a special index that is designed for doing range queries.
R-Trees are most commonly used in geospatial systems where each entry is a rectangle with minimum and maximum X and Y coordinates. Given a query rectangle, an R-Tree is able to quickly find all entries that are contained within the query rectangle or which overlap the query rectangle.
This idea is easily extended to three dimensions for use in CAD systems. R-Trees also find use in time-domain range look-ups. For example, suppose a database records the starting and ending times for a large number of events. A R-Tree is able to quickly find all events, for example, that were active at any time during a given time interval, or all events that started during a particular time interval, or all events that both started and ended within a given time interval. And so forth. See http://www.sqlite.org/rtree.html
Since the 2010-06-25 source code repository update, the RTREE extension is
compiled by default within all supplied .obj files of the
framework.
A dedicated ORM class, named TSQLRecordRTree, is available to
create such tables. It inherits from TSQLRecordVirtual, like the
other virtual tables types (e.g. TSQLRecordFTS3 or
our custom virtual
tables).
2011-06-01
2011-06-01. Open Source › mORMot Framework
According to the n-Tier architecture, data filtering and validation should be implemented in the business logic, not in the User Interface.
If you were used to develop RAD database application using Delphi, you may have to change a bit your habits here. Data filtering and validation should be implemented not in the User Interface, but in pure Delphi code.
Data filtering is a process run on the User entry: for instance, it will
trim left or right spaces, make the text uppercase...
Data validating is performed before saving the data to the database: for
instance, an email address is checked for consistency, a field value to be
unique...
Some try to implement this using an external
scripting engine, in a procedure/event mode. Back to the 80th...
In our ORM framework, filtering and validation can be performed by creating
some Delphi classes, which may be used on both Server and Client side.
