AWA_Counters
The Counters module defines a general purpose counter service that allows to
associate counters to database entities. For example it can be used to track the number
of times a blog post or a wiki page is accessed. The Counters module maintains the
counters in a table on a per-day and per-entity basis. It allows to update the full counter
in the target database entity table.
The Counter_Module manages the counters associated with database entities.
To avoid having to update the database each time a counter is incremented, counters
are kept temporarily in a Counter_Table protected type. The table contains
only the partial increments and not the real counter values. Counters are flushed
when the table reaches some limit, or, when the table is oldest than some limit.
Counters are associated with a day so that it becomes possible to gather per-day counters.
The table is also flushed when a counter is incremented in a different day.
An instance of the Counter_Module must be declared and registered in the
AWA application. The module instance can be defined as follows:
with AWA.Counters.Modules;
...
type Application is new AWA.Applications.Application with record
Counter_Module : aliased AWA.Counters.Modules.Counter_Module;
end record;And registered in the Initialize_Modules procedure by using:
Register (App => App.Self.all'Access,
Name => AWA.Counters.Modules.NAME,
Module => App.Counter_Module'Access);| Name | Description |
|---|---|
| counters.counter_age_limit | The maximum age limit in seconds for a pending counter increment to stay in the internal table. When a pending counter reaches this age limit, the pending counter increments are flushed and the table is cleared. The default is 5 minutes. |
| 300 | |
| counters.counter_limit | The maximum number of different counters which can be stored in the internal table before flushing the pending increments to the database. When this limit is reached, the pending counter increments are flushed and the table is cleared. |
| 1000 |
Each counter must be declared by instantiating the Definition package.
This instantiation serves as identification of the counter and it defines the database
table as well as the column in that table that will hold the total counter. The following
definition is used for the read counter of a wiki page. The wiki page table contains a
read_count column and it will be incremented each time the counter is incremented.
with AWA.Counters.Definition;
...
package Read_Counter is
new AWA.Counters.Definition (AWA.Wikis.Models.WIKI_PAGE_TABLE, "read_count");When the database table does not contain any counter column, the column field name is not given and the counter definition is defined as follows:
with AWA.Counters.Definition;
...
package Login_Counter is
new AWA.Counters.Definition (AWA.Users.Models.USER_PAGE_TABLE);Sometimes a counter is not associated with any database entity. Such counters are global and they are assigned a unique name.
with AWA.Counters.Definition;
...
package Start_Counter is
new AWA.Counters.Definition (null, "startup_counter");Incrementing the counter is done by calling the Increment operation.
When the counter is associated with a database entity, the entity primary key must be given.
The counter is not immediately incremented in the database so that several calls to the
Increment operation will not trigger a database update.
with AWA.Counters;
...
AWA.Counters.Increment (Counter => Read_Counter.Counter, Key => Id);A global counter is also incremented by using the Increment operation.
with AWA.Counters;
...
AWA.Counters.Increment (Counter => Start_Counter.Counter);The Counter_Bean allows to represent a counter associated with some database entity and allows its control by the awa:counter component.
The counter component is an Ada Server Faces component that allows to increment
and display easily the counter. The component works by using the Counter_Bean
Ada bean object which describes the counter in terms of counter definition, the
associated database entity, and the current counter value.
<awa:counter value="#{wikiPage.counter}"/>When the component is included in a page the Counter_Bean instance associated
with the EL value attribute is used to increment the counter. This is similar
to calling the AWA.Counters.Increment operation from the Ada code.
The Counters module has a simple database model which needs two tables.
The Counter_Definition table is used to keep track of the different counters
used by the application. A row in that table is created for each counter declared by
instantiating the Definition package. The Counter table holds the counters
for each database entity and for each day. By looking at that table, it becomes possible
to look at the daily access or usage of the counter.
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