This API is available on Firefox OS for internal applications 仅。
DataStoreTask
接口在
Data Store API
represents a record changed in the data store when a
DataStoreCursor
is used to iterate through the data store's change history.
注意 : The Data Store API is available in Web 工作者 , from Firefox 32 onwards (Firefox OS 2.0; see bug 949325 )。
DataStoreTask.data
只读
null
if the operation is
clear
or
done
.
DataStoreTask.id
只读
null
if the operation is
clear
or
done
.
DataStoreTask.operation
只读
Returns the type of operation that represents the current change that has been made to the data store.
DataStoreTask.revisionId
只读
Returns the id of the current revision of the data store, i.e. the current change that has been made to a data record.
In the following example, we use
navigator.getDataStores
to return a list of
DataStore
objects representing data stores on the device called
contacts
. Since there is only one such data store, we can access it inside the outer promise using
stores[0]
. The next promise uses
DataStore.getLength
to return the number of records in the store. If the value is 0, we populate the data store with records contained in the
contactsInit
object; if there is already data in the store, we run
DataStore.sync
to create a
DataStoreCursor
object allowing us to loop through any additions since the code last accessed the data store and update the data display as necessary.
The cursor is passed to the
runNextTask()
function, which calls
DataStoreCursor.next
to start the process of managing the next task — the resulting
DataStoreTask
object is passed to the
manageTask()
function to work out what to do with it.
runNextTask()
is then called repeatedly by
manageTask()
until the cursor has finished working through all the records.
navigator.getDataStores('contacts').then(function(stores) {
stores[0].getLength().then(function(storeLength) {
if(storeLength == 0) {
for(i = 0; i < contactsInit.length; i++) {
addContact(stores[0],contactsInit[i]);
};
} else {
var cursor = stores[0].sync();
runNextTask(cursor);
}
});
});
function runNextTask(cursor) {
cursor.next().then(function(task) {
manageTask(cursor, task);
});
}
function manageTask(cursor, task) {
if (task.operation == 'done') {
// Finished adding contacts!
return;
}
if (task.operation == 'add') {
// Add the contacts that are different to how it was before
displayExisting(task.id, task.data);
}
runNextTask(cursor);
}
注意 : This code is taken from our Data Store Contacts Editor demo. Look through the code to help you understand better what is going on, and how the full code works.
The different operation types used in
DataStoreTask
are (see also the
spec definitions
):
| Enumeration | 描述 |
|---|---|
add
|
The data record is added into the data store. |
update
|
The data record is updated in the data store. |
remove
|
The data record is deleted in the data store. |
clear
|
All the records are deleted from the data store; a
clear
operation (plus a list of
add
operations) is also received when the revision ID is too old for the DataStore to be able to provide all the steps to bring you to the current ID. The DataStore Service has a list of about 100 operations in memory.
|
done
|
All changes are finished. |
注意
: These are currently different to the operation types returned by
DataStoreChangeEvent
. This discrepancy will be fixed soon at an appropriate time.
| 规范 | 状态 | 注释 |
|---|---|---|
|
Data Store API
The definition of 'DataStoreTask' in that specification. |
草案 |
The discussion concerning this API's creation happened in various Mozilla mailing lists and other places. A summary of the discussion and further pointers can be found on the Mozilla Wiki . For further feedback and questions, send mail to the dev-webapi mailing list.