Elektra  0.8.11
Public Member Functions
kdb::KDB Class Reference

Constructs a class KDB. More...

#include <kdb.hpp>

Public Member Functions

 KDB ()
 Constructs a class KDB.
 
 KDB (Key &errorKey)
 Constructs a class KDB.
 
 ~KDB () throw ()
 The destructor closes the database.
 
void open (Key &errorKey)
 Open the database.
 
void close (Key &errorKey) throw ()
 Open the database.
 
int get (KeySet &returned, std::string const &keyname)
 Get all keys below keyname inside returned.
 
int get (KeySet &returned, Key &parentKey)
 Get all keys below parentKey inside returned.
 
int set (KeySet &returned, std::string const &keyname)
 Set all keys below keyname.
 
int set (KeySet &returned, Key &parentKey)
 Set all keys below parentKey.
 

Detailed Description

Constructs a class KDB.

Exceptions
KDBExceptionif database could not be opened

Opens the session with the Key database.

Precondition
errorKey must be a valid key, e.g. created with keyNew()

The method will bootstrap itself the following way. The first step is to open the default backend. With it system/elektra/mountpoints will be loaded and all needed libraries and mountpoints will be determined. These libraries for backends will be loaded and with it the KDB datastructure will be initialized.You must always call this method before retrieving or committing any keys to the database. In the end of the program, after using the key database, you must not forget to kdbClose().The pointer to the KDB structure returned will be initialized like described above, and it must be passed along on any kdb*() method your application calls.Get a KDB handle for every thread using elektra. Don't share the handle across threads, and also not the pointer accessing it:

void thread1()
{
Key *parent = keyNew("/app/part1", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}
void thread2()
{
Key *parent = keyNew("/app/part2", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}

You don't need kdbOpen() if you only want to manipulate plain in-memory Key or KeySet objects.

Precondition
errorKey must be a valid key, e.g. created with keyNew()
Parameters
errorKeythe key which holds errors and warnings which were issued
See Also
kdbGet(), kdbClose() to end all affairs to the Key database.
Return values
handleon success
NULLon failure

Access to the key database.

Invariant
the object holds an valid connection to the key database or is empty

Constructor & Destructor Documentation

kdb::KDB::KDB ( )
inline

Constructs a class KDB.

Exceptions
KDBExceptionif database could not be opened

Opens the session with the Key database.

Precondition
errorKey must be a valid key, e.g. created with keyNew()

The method will bootstrap itself the following way. The first step is to open the default backend. With it system/elektra/mountpoints will be loaded and all needed libraries and mountpoints will be determined. These libraries for backends will be loaded and with it the KDB datastructure will be initialized.You must always call this method before retrieving or committing any keys to the database. In the end of the program, after using the key database, you must not forget to kdbClose().The pointer to the KDB structure returned will be initialized like described above, and it must be passed along on any kdb*() method your application calls.Get a KDB handle for every thread using elektra. Don't share the handle across threads, and also not the pointer accessing it:

void thread1()
{
Key *parent = keyNew("/app/part1", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}
void thread2()
{
Key *parent = keyNew("/app/part2", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}

You don't need kdbOpen() if you only want to manipulate plain in-memory Key or KeySet objects.

Precondition
errorKey must be a valid key, e.g. created with keyNew()
Parameters
errorKeythe key which holds errors and warnings which were issued
See Also
kdbGet(), kdbClose() to end all affairs to the Key database.
Return values
handleon success
NULLon failure

kdb::KDB::KDB ( Key errorKey)
inline

Constructs a class KDB.

Parameters
errorKeyis useful if you want to get the warnings in the successful case, when no exception is thrown.
Exceptions
KDBExceptionif database could not be opened

Opens the session with the Key database.

Precondition
errorKey must be a valid key, e.g. created with keyNew()

The method will bootstrap itself the following way. The first step is to open the default backend. With it system/elektra/mountpoints will be loaded and all needed libraries and mountpoints will be determined. These libraries for backends will be loaded and with it the KDB datastructure will be initialized.You must always call this method before retrieving or committing any keys to the database. In the end of the program, after using the key database, you must not forget to kdbClose().The pointer to the KDB structure returned will be initialized like described above, and it must be passed along on any kdb*() method your application calls.Get a KDB handle for every thread using elektra. Don't share the handle across threads, and also not the pointer accessing it:

void thread1()
{
Key *parent = keyNew("/app/part1", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}
void thread2()
{
Key *parent = keyNew("/app/part2", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}

You don't need kdbOpen() if you only want to manipulate plain in-memory Key or KeySet objects.

Precondition
errorKey must be a valid key, e.g. created with keyNew()
Parameters
errorKeythe key which holds errors and warnings which were issued
See Also
kdbGet(), kdbClose() to end all affairs to the Key database.
Return values
handleon success
NULLon failure

kdb::KDB::~KDB ( ) throw ()
inline

The destructor closes the database.

Closes the session with the Key database.

Precondition
The handle must be a valid handle as returned from kdbOpen()
errorKey must be a valid key, e.g. created with keyNew()

This is the counterpart of kdbOpen().You must call this method when you finished your affairs with the key database. You can manipulate Key and KeySet objects also after kdbClose(), but you must not use any kdb*() call afterwards.The handle parameter will be finalized and all resources associated to it will be freed. After a kdbClose(), the handle cannot be used anymore.

Parameters
handlecontains internal information of opened key database
errorKeythe key which holds error/warning information
Return values
0on success
-1on NULL pointer

Member Function Documentation

void kdb::KDB::close ( Key errorKey) throw ()
inline

Open the database.

The return value does not matter because its only a null pointer check.

Parameters
errorKeyis useful if you want to get the warnings

Closes the session with the Key database.

Precondition
The handle must be a valid handle as returned from kdbOpen()
errorKey must be a valid key, e.g. created with keyNew()

This is the counterpart of kdbOpen().You must call this method when you finished your affairs with the key database. You can manipulate Key and KeySet objects also after kdbClose(), but you must not use any kdb*() call afterwards.The handle parameter will be finalized and all resources associated to it will be freed. After a kdbClose(), the handle cannot be used anymore.

Parameters
handlecontains internal information of opened key database
errorKeythe key which holds error/warning information
Return values
0on success
-1on NULL pointer

int kdb::KDB::get ( KeySet returned,
std::string const &  keyname 
)
inline

Get all keys below keyname inside returned.

Retrieve keys in an atomic and universal way.

Precondition
The handle must be passed as returned from kdbOpen()
The returned KeySet must be a valid KeySet, e.g. constructed with ksNew().
The parentKey Key must be a valid Key, e.g. constructed with keyNew().

If you pass NULL, which violates the preconditions, on any parameter kdbGet() will fail immediately without doing anything.The returned KeySet may already contain some keys, e.g. from previous kdbGet() calls. The new retrieved keys will be appended using ksAppendKey().It will fully retrieve, at least, all keys under the parentKey folder, with all subfolders and their children.

Note
kdbGet() might retrieve more keys then requested (that are not below parentKey). These keys must be passed to calls of kdbSet(), otherwise they will be lost. This stems from the fact that the user has the only copy of the whole configuration and backends only write configuration that was passed to them. For example, if you kdbGet() "system/mountpoint/interest" you will not only get all keys below system/mountpoint/interest, but also all keys below system/mountpoint (if system/mountpoint is a mountpoint as the name suggests, but system/mountpoint/interest is not a mountpoint). Make sure to not touch or remove keys outside the keys of interest, because others may need them!
Example:
This example demonstrates the typical usecase within an application (without error handling).
#include <kdb.h>
#include <stdio.h>
int main()
{
KeySet *myConfig = ksNew(0, KS_END);
Key *key = keyNew("/sw/MyApp", KEY_CASCADING_NAME, KEY_END);
KDB *handle = kdbOpen(key);
kdbGet(handle, myConfig, key);
// TODO: check for errors and warnings in key
keyDel(key);
Key * result = ksLookupByName(myConfig,"/sw/MyApp/Tests/TestKey1", 0);
// TODO: check if result is not 0 and work with it...
const char * key_name = keyName(result);
const char * key_value = keyString(result);
const char * key_comment = keyString(keyGetMeta(result, "comment"));
printf("key: %s value: %s comment: %s\n", key_name, key_value, key_comment);
ksDel (myConfig); // delete the in-memory configuration
// maybe you want kdbSet() myConfig here
kdbClose(handle, 0); // no more affairs with the key database.
}
When a backend fails kdbGet() will return -1 with all error and warning information in the parentKey. The parameter returned will not be changed.
Updates:
In the first run of kdbGet all requested (or more) keys are retrieved. On subsequent calls only the keys are retrieved where something was changed inside the key database. The other keys stay unchanged in the keyset, even if they were manipulated.

It is your responsibility to save the original keyset if you need it afterwards.If you want to get the same keyset again, you need to open a second handle to the key database using kdbOpen().

Parameters
handlecontains internal information of opened key database
parentKeyis used to add warnings and set an error information. Additionally, its name is an hint which keys should be retrieved (it is possible that more are retrieved).
  • cascading keys (starting with /) will retrieve the same path in all namespaces
  • / will retrieve all keys
ksthe (pre-initialized) KeySet returned with all keys found will not be changed on error or if no update is required
See Also
ksLookup(), ksLookupByName() for powerful lookups after the KeySet was retrieved
kdbOpen() which needs to be called before
kdbSet() to save the configuration afterwards and kdbClose() to finish affairs with the Key database.
Return values
1if the keys were retrieved successfully
0if there was no update - no changes are made to the keyset then
-1on failure - no changes are made to the keyset then

#include <kdb.hpp>
#include <keyio.hpp>
using namespace kdb;
int main()
{
KeySet config;
KDB kdb;
kdb.get(config, "/sw/MyApp");
Key k = config.lookup("/sw/MyApp/mykey");
if (k)
{
std::cout << k << " is " << k.get<int>() << std::endl;
}
else
{
std::cerr << "No key found" << std::endl;
return 1;
}
}
Parameters
returnedthe keyset where the keys will be in
keynamethe root keyname which should be used to get keys below it

Return values
0if no key was updated
1if user or system keys were updated
2if user and system keys were updated

Exceptions
KDBExceptionif there were problems with the database
See Also
KDB::get (KeySet & returned, Key & parentKey)
int kdb::KDB::get ( KeySet returned,
Key parentKey 
)
inline

Get all keys below parentKey inside returned.

Retrieve keys in an atomic and universal way.

Precondition
The handle must be passed as returned from kdbOpen()
The returned KeySet must be a valid KeySet, e.g. constructed with ksNew().
The parentKey Key must be a valid Key, e.g. constructed with keyNew().

If you pass NULL, which violates the preconditions, on any parameter kdbGet() will fail immediately without doing anything.The returned KeySet may already contain some keys, e.g. from previous kdbGet() calls. The new retrieved keys will be appended using ksAppendKey().It will fully retrieve, at least, all keys under the parentKey folder, with all subfolders and their children.

Note
kdbGet() might retrieve more keys then requested (that are not below parentKey). These keys must be passed to calls of kdbSet(), otherwise they will be lost. This stems from the fact that the user has the only copy of the whole configuration and backends only write configuration that was passed to them. For example, if you kdbGet() "system/mountpoint/interest" you will not only get all keys below system/mountpoint/interest, but also all keys below system/mountpoint (if system/mountpoint is a mountpoint as the name suggests, but system/mountpoint/interest is not a mountpoint). Make sure to not touch or remove keys outside the keys of interest, because others may need them!
Example:
This example demonstrates the typical usecase within an application (without error handling).
#include <kdb.h>
#include <stdio.h>
int main()
{
KeySet *myConfig = ksNew(0, KS_END);
Key *key = keyNew("/sw/MyApp", KEY_CASCADING_NAME, KEY_END);
KDB *handle = kdbOpen(key);
kdbGet(handle, myConfig, key);
// TODO: check for errors and warnings in key
keyDel(key);
Key * result = ksLookupByName(myConfig,"/sw/MyApp/Tests/TestKey1", 0);
// TODO: check if result is not 0 and work with it...
const char * key_name = keyName(result);
const char * key_value = keyString(result);
const char * key_comment = keyString(keyGetMeta(result, "comment"));
printf("key: %s value: %s comment: %s\n", key_name, key_value, key_comment);
ksDel (myConfig); // delete the in-memory configuration
// maybe you want kdbSet() myConfig here
kdbClose(handle, 0); // no more affairs with the key database.
}
When a backend fails kdbGet() will return -1 with all error and warning information in the parentKey. The parameter returned will not be changed.
Updates:
In the first run of kdbGet all requested (or more) keys are retrieved. On subsequent calls only the keys are retrieved where something was changed inside the key database. The other keys stay unchanged in the keyset, even if they were manipulated.

It is your responsibility to save the original keyset if you need it afterwards.If you want to get the same keyset again, you need to open a second handle to the key database using kdbOpen().

Parameters
handlecontains internal information of opened key database
parentKeyis used to add warnings and set an error information. Additionally, its name is an hint which keys should be retrieved (it is possible that more are retrieved).
  • cascading keys (starting with /) will retrieve the same path in all namespaces
  • / will retrieve all keys
ksthe (pre-initialized) KeySet returned with all keys found will not be changed on error or if no update is required
See Also
ksLookup(), ksLookupByName() for powerful lookups after the KeySet was retrieved
kdbOpen() which needs to be called before
kdbSet() to save the configuration afterwards and kdbClose() to finish affairs with the Key database.
Return values
1if the keys were retrieved successfully
0if there was no update - no changes are made to the keyset then
-1on failure - no changes are made to the keyset then

Parameters
returnedthe keyset where the keys will be in
parentKeythe parentKey of returned

Return values
0if no key was updated
1if user or system keys were updated
2if user and system keys were updated

Exceptions
KDBExceptionif there were problems with the database
void kdb::KDB::open ( Key errorKey)
inline

Open the database.

Parameters
errorKeyis useful if you want to get the warnings in the successful case, when no exception is thrown.

Opens the session with the Key database.

Precondition
errorKey must be a valid key, e.g. created with keyNew()

The method will bootstrap itself the following way. The first step is to open the default backend. With it system/elektra/mountpoints will be loaded and all needed libraries and mountpoints will be determined. These libraries for backends will be loaded and with it the KDB datastructure will be initialized.You must always call this method before retrieving or committing any keys to the database. In the end of the program, after using the key database, you must not forget to kdbClose().The pointer to the KDB structure returned will be initialized like described above, and it must be passed along on any kdb*() method your application calls.Get a KDB handle for every thread using elektra. Don't share the handle across threads, and also not the pointer accessing it:

void thread1()
{
Key *parent = keyNew("/app/part1", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}
void thread2()
{
Key *parent = keyNew("/app/part2", KEY_CASCADING_NAME, KEY_END);
KDB * h = kdbOpen(parent);
// fetch keys and work with them
kdbClose(h, parent);
}

You don't need kdbOpen() if you only want to manipulate plain in-memory Key or KeySet objects.

Precondition
errorKey must be a valid key, e.g. created with keyNew()
Parameters
errorKeythe key which holds errors and warnings which were issued
See Also
kdbGet(), kdbClose() to end all affairs to the Key database.
Return values
handleon success
NULLon failure

int kdb::KDB::set ( KeySet returned,
std::string const &  keyname 
)
inline

Set all keys below keyname.

If the keyname of the parentKey is invalid (e.g. empty) all keys will be set.

Set keys in an atomic and universal way.

Precondition
kdbGet() must be called before kdbSet():
The returned KeySet must be a valid KeySet, e.g. constructed with ksNew().
The parentKey Key must be a valid Key, e.g. constructed with

With parentKey you can give an hint which part of the given keyset is of interest for you. Then you promise, you only modified or removed keys below this key.

Errors
If some error occurs, kdbSet() will stop. In this situation the KeySet internal cursor will be set on the key that generated the error. None of the keys are actually committed in this situation (no configuration file will be modified).

In case of errors you should present the error message to the user and let the user decide what to do. Possible solutions are:

  • remove the problematic key and use kdbSet() again (for validation or type errors)
  • change the value of the problematic key and use kdbSet() again (for validation errors)
  • do a kdbGet() (for conflicts, i.e. error 30) and then
    • set the same keyset again (in favour of what was set by this user)
    • drop the old keyset (in favour of what was set from another application)
    • merge the original, your own and the other keyset
  • export the configuration into a file (for unresolvable errors)
  • repeat the same kdbSet might be of limited use if the operator does not explicitly request it, because temporary errors are rare and its unlikely that they fix themselves (e.g. disc full, permission problems)
Optimization
Each key is checked with keyNeedSync() before being actually committed. So only changed keys are updated. If no key of a backend needs to be synced any affairs to backends are omitted and 0 is returned.
KeySet *myConfig = ksNew(0, KS_END);
Key *parentKey = keyNew("system/sw/MyApp",KEY_END);
KDB *handle = kdbOpen(parentKey);
kdbGet(handle, myConfig, parentKey); // kdbGet needs to be called first!
KeySet *base = ksDup(myConfig); // save a copy of original keyset
// change the keys within myConfig
KeySet *ours = ksDup(myConfig); // save a copy of our keyset
int ret=kdbSet(handle, myConfig, parentKey);
while (ret == -1) // as long as we have an error
{
// We got an error. Warn user.
Key *problemKey = ksCurrent(myConfig);
// parentKey has the errorInformation
// problemKey is the faulty key (may be null)
int userInput = showElektraErrorDialog (parentKey, problemKey);
switch (userInput)
{
case INPUT_USE_OURS:
kdbGet(handle, myConfig, parentKey); // refresh key database
ksDel(myConfig);
myConfig = ours;
break;
case INPUT_DO_MERGE:
kdbGet(handle, myConfig, parentKey); // refresh key database
KeySet * res=doElektraMerge(ours, myConfig, base);
ksDel(myConfig);
myConfig = res;
break;
case INPUT_USE_THEIRS:
// should always work, we just write what we got
// but to be sure always give the user another way
// to exit the loop
kdbGet(handle, myConfig, parentKey); // refresh key database
break;
// other cases ...
}
ret=kdbSet(handle, myConfig, parentKey);
}
ksDel (ours);
ksDel (base);
ksDel (myConfig); // delete the in-memory configuration
kdbClose(handle, parentKey); // no more affairs with the key database.
keyDel(parentKey);

showElektraErrorDialog() and doElektraMerge() need to be implemented by the user of Elektra. For doElektraMerge a 3-way merge algorithm exists in libelektra-tools.

Parameters
handlecontains internal information of opened key database
ksa KeySet which should contain changed keys, otherwise nothing is done
parentKeyis used to add warnings and set an error information. Additionally, its name is an hint which keys should be committed (it is possible that more are changed).
  • cascading keys (starting with /) will set the path in all namespaces
  • / will commit all keys
  • meta-names will be rejected (error 104)
  • empty/invalid (error 105)
Return values
1on success
0if nothing had to be done, no changes in KDB
-1on failure, no changes in KDB
See Also
keyNeedSync()
ksCurrent() contains the error Key
kdbOpen() and kdbGet() that must be called first
kdbClose() that must be called afterwards

Return values
0if no key was updated
1if user or system keys were updated
2if user and system keys were updated

Parameters
returnedthe keyset where the keys will be in
keynamethe keyname below the names should be set
Exceptions
KDBExceptionif there were problems with the database
int kdb::KDB::set ( KeySet returned,
Key parentKey 
)
inline

Set all keys below parentKey.

If the keyname of the parentKey is invalid (e.g. empty) all keys will be set.

Set keys in an atomic and universal way.

Precondition
kdbGet() must be called before kdbSet():
The returned KeySet must be a valid KeySet, e.g. constructed with ksNew().
The parentKey Key must be a valid Key, e.g. constructed with

With parentKey you can give an hint which part of the given keyset is of interest for you. Then you promise, you only modified or removed keys below this key.

Errors
If some error occurs, kdbSet() will stop. In this situation the KeySet internal cursor will be set on the key that generated the error. None of the keys are actually committed in this situation (no configuration file will be modified).

In case of errors you should present the error message to the user and let the user decide what to do. Possible solutions are:

  • remove the problematic key and use kdbSet() again (for validation or type errors)
  • change the value of the problematic key and use kdbSet() again (for validation errors)
  • do a kdbGet() (for conflicts, i.e. error 30) and then
    • set the same keyset again (in favour of what was set by this user)
    • drop the old keyset (in favour of what was set from another application)
    • merge the original, your own and the other keyset
  • export the configuration into a file (for unresolvable errors)
  • repeat the same kdbSet might be of limited use if the operator does not explicitly request it, because temporary errors are rare and its unlikely that they fix themselves (e.g. disc full, permission problems)
Optimization
Each key is checked with keyNeedSync() before being actually committed. So only changed keys are updated. If no key of a backend needs to be synced any affairs to backends are omitted and 0 is returned.
KeySet *myConfig = ksNew(0, KS_END);
Key *parentKey = keyNew("system/sw/MyApp",KEY_END);
KDB *handle = kdbOpen(parentKey);
kdbGet(handle, myConfig, parentKey); // kdbGet needs to be called first!
KeySet *base = ksDup(myConfig); // save a copy of original keyset
// change the keys within myConfig
KeySet *ours = ksDup(myConfig); // save a copy of our keyset
int ret=kdbSet(handle, myConfig, parentKey);
while (ret == -1) // as long as we have an error
{
// We got an error. Warn user.
Key *problemKey = ksCurrent(myConfig);
// parentKey has the errorInformation
// problemKey is the faulty key (may be null)
int userInput = showElektraErrorDialog (parentKey, problemKey);
switch (userInput)
{
case INPUT_USE_OURS:
kdbGet(handle, myConfig, parentKey); // refresh key database
ksDel(myConfig);
myConfig = ours;
break;
case INPUT_DO_MERGE:
kdbGet(handle, myConfig, parentKey); // refresh key database
KeySet * res=doElektraMerge(ours, myConfig, base);
ksDel(myConfig);
myConfig = res;
break;
case INPUT_USE_THEIRS:
// should always work, we just write what we got
// but to be sure always give the user another way
// to exit the loop
kdbGet(handle, myConfig, parentKey); // refresh key database
break;
// other cases ...
}
ret=kdbSet(handle, myConfig, parentKey);
}
ksDel (ours);
ksDel (base);
ksDel (myConfig); // delete the in-memory configuration
kdbClose(handle, parentKey); // no more affairs with the key database.
keyDel(parentKey);

showElektraErrorDialog() and doElektraMerge() need to be implemented by the user of Elektra. For doElektraMerge a 3-way merge algorithm exists in libelektra-tools.

Parameters
handlecontains internal information of opened key database
ksa KeySet which should contain changed keys, otherwise nothing is done
parentKeyis used to add warnings and set an error information. Additionally, its name is an hint which keys should be committed (it is possible that more are changed).
  • cascading keys (starting with /) will set the path in all namespaces
  • / will commit all keys
  • meta-names will be rejected (error 104)
  • empty/invalid (error 105)
Return values
1on success
0if nothing had to be done, no changes in KDB
-1on failure, no changes in KDB
See Also
keyNeedSync()
ksCurrent() contains the error Key
kdbOpen() and kdbGet() that must be called first
kdbClose() that must be called afterwards

Return values
0if no key was updated
1if user or system keys were updated
2if user and system keys were updated

Parameters
returnedthe keyset where the keys are passed to the user
parentKeythe parentKey of returned
Exceptions
KDBExceptionif there were problems with the database

The documentation for this class was generated from the following file: