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

KDBException

if 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

errorKey

the key which holds errors and warnings which were issued

See Also

kdbGet(), kdbClose() to end all affairs to the Key database.

Return values

handle	on success
NULL	on 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

KDBException

if 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

errorKey

the key which holds errors and warnings which were issued

See Also

kdbGet(), kdbClose() to end all affairs to the Key database.

Return values

handle	on success
NULL	on failure

kdb::KDB::KDB ( Key &  errorKey )

inline

Constructs a class KDB.

Parameters

errorKey

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

Exceptions

KDBException

if 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

errorKey

the key which holds errors and warnings which were issued

See Also

kdbGet(), kdbClose() to end all affairs to the Key database.

Return values

handle	on success
NULL	on 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

handle	contains internal information of opened key database
errorKey	the key which holds error/warning information

Return values

0	on success
-1	on 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

errorKey

is 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

handle	contains internal information of opened key database
errorKey	the key which holds error/warning information

Return values

0	on success
-1	on 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);
        // to get an intention of proper error handling see kdbget_error.c

        keyDel (key);

        Key * result = ksLookupByName (myConfig,"/sw/MyApp/Tests/TestKey1", 0);

        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

handle	contains internal information of opened key database
parentKey	is 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
ks	the (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

1	if the keys were retrieved successfully
0	if there was no update - no changes are made to the keyset then
-1	on 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

returned	the keyset where the keys will be in
keyname	the root keyname which should be used to get keys below it

Return values

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

Exceptions

KDBException

if 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);
        // to get an intention of proper error handling see kdbget_error.c

        keyDel (key);

        Key * result = ksLookupByName (myConfig,"/sw/MyApp/Tests/TestKey1", 0);

        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

handle	contains internal information of opened key database
parentKey	is 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
ks	the (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

1	if the keys were retrieved successfully
0	if there was no update - no changes are made to the keyset then
-1	on failure - no changes are made to the keyset then

Parameters

returned	the keyset where the keys will be in
parentKey	the parentKey of returned

Return values

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

Exceptions

KDBException

if there were problems with the database

void kdb::KDB::open ( Key &  errorKey )

inline

Open the database.

Parameters

errorKey

is 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

errorKey

the key which holds errors and warnings which were issued

See Also

kdbGet(), kdbClose() to end all affairs to the Key database.

Return values

handle	on success
NULL	on 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():

• initially (after kdbOpen())
• after conflict errors in 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

handle	contains internal information of opened key database
ks	a KeySet which should contain changed keys, otherwise nothing is done
parentKey	is 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

1	on success
0	if nothing had to be done, no changes in KDB
-1	on 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

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

Parameters

returned	the keyset where the keys will be in
keyname	the keyname below the names should be set

Exceptions

KDBException

if 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():

• initially (after kdbOpen())
• after conflict errors in 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

handle	contains internal information of opened key database
ks	a KeySet which should contain changed keys, otherwise nothing is done
parentKey	is 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

1	on success
0	if nothing had to be done, no changes in KDB
-1	on 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

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

Parameters

returned	the keyset where the keys are passed to the user
parentKey	the parentKey of returned

Exceptions

KDBException

if there were problems with the database

---

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

• kdb.hpp