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Triggers

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Philippe Pittoli 2025-01-24 17:14:11 +01:00
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@ -315,8 +315,11 @@ The above code presents the creation of a new index on the database
.I cars . .I cars .
An index requires a name (a simple string), which simply is "name" in this case since the indexed value is the name of the cars. An index requires a name (a simple string), which simply is "name" in this case since the indexed value is the name of the cars.
An index also requires a callback, a procedure to extract the value used for indexing. An index also requires a callback, a procedure to extract the value used for indexing.
In this case, the procedure takes a car as a parameter and returns its "name" attribute. In this case, the procedure takes a car as a parameter and returns its "name" attribute\*[*].
This procedure can be arbitrary complex and include any necessary data transformation. .FOOTNOTE1
This procedure can be arbitrarily complex and include any necessary data transformation.
For example, the netlibre project (discussed later in the papper) indexes their users' email, but emails are first encoded in base64 to avoid messing around with the file-system.
.FOOTNOTE2
Once the index has been created, every inserted or modified entry in the database will be indexed. Once the index has been created, every inserted or modified entry in the database will be indexed.
Adding a trigger provides an Adding a trigger provides an
@ -390,8 +393,8 @@ end
# Shortcut: # Shortcut:
cars_by_color = database.new_partition "color", &.color cars_by_color = database.new_partition "color", &.color
.SOURCE .SOURCE
.QE
As with basic indexes, once the partition is asked to the database, every new or modified entry will be indexed. As with basic indexes, once the partition is asked to the database, every new or modified entry will be indexed.
.QE
.KS .KS
Let's imagine having 3 cars, one is blue and the other two are red. Let's imagine having 3 cars, one is blue and the other two are red.
@ -463,17 +466,26 @@ Listing all the fast cars is simple as running
in the in the
.DIRECTORY db-cars/tags/by_keywords/fast .DIRECTORY db-cars/tags/by_keywords/fast
directory! directory!
And only a simple intersection of the files that are several directories is necessary to get cars which are both fast and cheap for example\*[*].
.QE .QE
.KE .KE
.FOOTNOTE1
A simple command is necessary to get cars that are both fast and cheap:
.br
.COMMAND "ls fast/* cheap/* | cut -f 2 -d '/' | sort | uniq -c | awk '{ print $1, $2 }' | grep ^2"
.br
This may appear barbaric for the unprepared mind, but this one-liner only includes basic commands most sysadmin understand and perhaps use daily.
Also, this can be as easily hidden in a very nice user-friendly command.
.FOOTNOTE2
. .
. .
. .
.SSS Side note about triggers .SSS Side note about triggers
DODB presents a few possible triggers (basic indexes, partitions and tags) which respond to an obvious need for fast searches. DODB presents a few possible triggers (basic indexes, partitions and tags) which respond to an obvious need for fast searches and retrevial.
Though, their implementation via the creation of symlinks is the result of a certain vision about how a database should behave in order to provide a practical way for users to sort the entries. Though, their implementation via the creation of symlinks is the result of a certain vision about how a database should behave in order to provide a practical way for users to play with the entries outside the application.
The implementation can be completely changed. The implementation can be completely changed.
Also, other kinds of triggers could Other kinds of triggers could
.B easily .B easily
be implemented in addition of those presented. be implemented in addition of those presented.
The new triggers may have completely different objectives than providing a file-system representation of the data. The new triggers may have completely different objectives than providing a file-system representation of the data.