This is the legacy 4D documentation web site. Documentations are progressively being moved to developer.4d.com
- 4D Language Reference
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- Database Methods
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Database Methods
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On Backup Shutdown database method
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On Backup Startup database method
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On Drop database method
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On Exit database method
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On Host Database Event database method
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On Mobile App Action database method
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On Mobile App Authentication database method
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On Server Close Connection database method
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On Server Open Connection database method
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On Server Shutdown database method
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On Server Startup database method
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On SQL Authentication database method
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On Startup database method
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On System Event database method
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On Web Authentication database method
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On Web Connection database method
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On Web Legacy Close Session database method
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On REST Authentication database method
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On Host Database Event database method
| $1 -> On Host Database Event database method | ||||||||
| Parameter | Type | Description | ||||||
| $1 | Longint |
|
Event code | |||||
The On Host Database Event database method allows 4D components to execute code when the host database is opened and closed.
Note: For security reasons, in order to be able to call this database method, you must explicitly allow its execution in the host database. For more information about this point, refer to the Design Reference manual.
The On Host Database Event database method is executed automatically only in databases used as components of host databases (when it is authorized in the Settings of the host database). It is called when events related to the opening and closing of the host database occur.
To process an event, you must test the value of the $1 parameter inside the method, and compare it with one of the following constants, available in the "Database Events" theme:
| Constant | Type | Value | Comment |
| On after host database exit | Longint | 4 | The On Exit database method of the host database has just finished running |
| On after host database startup | Longint | 2 | The On Startup database method of the host database just finished running |
| On before host database exit | Longint | 3 | The host database is closing. The On Exit database method of the host database has not yet been called. |
| On before host database startup | Longint | 1 | The host database has just been started. The On Startup database method method of the host database has not yet been called. |
This allows 4D components to load and save preferences or user states related to the operation of the host database.
Example of typical structure of an On Host Database Event database method:
// On Host Database Event database method
C_LONGINT($1)
Case of
:($1=On before host database startup)
// put code here that you want to execute before the "On Startup" database method
// of the host database
:($1=On after host database startup)
// put code here that you want to execute after the "On Startup"
// database method of the host database
:($1=On before host database exit)
// put code here that you want to execute before the "On Exit"
// database method of the host database
:($1=On after host database exit)
// put code here that you want to execute after the "On Exit"
// database method of the host database
End case
Product: 4D
Theme: Database Methods
Created: 4D v14
4D Language Reference ( 4D v20 R7)
