The first element is the parameter number; the second is the value to be set. In this case, the first element of params is 1 , , and the second element is 2 , "West".
When an application calls the method execute , it will in turn call on this RowSet object's reader, which will in turn invoke its readData method. As part of its implementation, readData will get the values in params and use them to set the command's placeholder parameters. The following code fragment gives an idea of how the reader does this, after obtaining the Connection object con. After the readData method executes this command with the following line of code, it will have the data from rs with which to populate crs.
In contrast, the following code fragment shows what an application might do. It sets the rowset's command, sets the command's parameters, and executes the command.
To get around this limitation, a CachedRowSet object can retrieve data from a ResultSet object in chunks of data, called pages. To take advantage of this mechanism, an application sets the number of rows to be included in a page using the method setPageSize. In other words, if the page size is set to five, a chunk of five rows of data will be fetched from the data source at one time. An application can also optionally set the maximum number of rows that may be fetched at one time.
If the maximum number of rows is set to zero, or no maximum number of rows is set, there is no limit to the number of rows that may be fetched at a time. After properties have been set, the CachedRowSet object must be populated with data using either the method populate or the method execute.
The following lines of code demonstrate using the method populate. Note that this version of the method takes two parameters, a ResultSet handle and the row in the ResultSet object from which to start retrieving rows. The next code fragment shows populating a CachedRowSet object using the method execute , which may or may not take a Connection object as a parameter.
This code passes execute the Connection object conHandle. Note that there are two differences between the following code fragment and the previous one. First, the method setMaxRows is not called, so there is no limit set for the number of rows that crs may contain. Remember that crs always has the overriding limit of how much data it can store in memory.
The second difference is that the you cannot pass the method execute the number of the row in the ResultSet object from which to start retrieving rows. This method always starts with the first row.
The writer for crs will use conHandle to connect to the data source and execute the command for crs. An application is then able to operate on the data in crs in the same way that it would operate on data in any other CachedRowSet object. To access the next page chunk of data , an application calls the method nextPage.
This method creates a new CachedRowSet object and fills it with the next page of data. For example, assume that the CachedRowSet object's command returns a ResultSet object rs with rows of data. If the page size has been set to , the first call to the method nextPage will create a CachedRowSet object containing the first rows of rs.
After doing what it needs to do with the data in these first rows, the application can again call the method nextPage to create another CachedRowSet object with the second rows from rs.
The data from the first CachedRowSet object will no longer be in memory because it is replaced with the data from the second CachedRowSet object. After the tenth call to the method nextPage , the tenth CachedRowSet object will contain the last rows of data from rs , which are stored in memory.
At any given time, the data from only one CachedRowSet object is stored in memory. The method nextPage returns true as long as the current page is not the last page of rows and false when there are no more pages. It can therefore be used in a while loop to retrieve all of the pages, as is demonstrated in the following lines of code. The CachedRowSet interface also defines the method previousPage. Just as the method nextPage is analogous to the ResultSet method next , the method previousPage is analogous to the ResultSet method previous.
Similar to the method nextPage , previousPage creates a CachedRowSet object containing the number of rows set as the page size. So, for instance, the method previousPage could be used in a while loop at the end of the preceding code fragment to navigate back through the pages from the last page to the first page. The method previousPage is also similar to nextPage in that it can be used in a while loop, except that it returns true as long as there is another page preceding it and false when there are no more pages ahead of it.
By positioning the cursor after the last row for each page, as is done in the following code fragment, the method previous navigates from the last row to the first row in each page. The code could also have left the cursor before the first row on each page and then used the method next in a while loop to navigate each page from the first row to the last row. The following code fragment assumes a continuation from the previous code fragment, meaning that the cursor for the tenth CachedRowSet object is on the last row.
The code moves the cursor to after the last row so that the first call to the method previous will put the cursor back on the last row. After going through all of the rows in the last page the CachedRowSet object crs , the code then enters the while loop to get to the ninth page, go through the rows backwards, go to the eighth page, go through the rows backwards, and so on to the first row of the first page.
Because this field is final it is part of an interface , its value cannot be changed. Fields inherited from interface java. Methods inherited from interface javax. Wrapper isWrapperFor , unwrap Methods inherited from interface javax. If set to false, the changes will not be committed until one of the CachedRowSet interface transaction methods is called. This method can be used as an alternative to the execute method when an application has a connection to an open ResultSet object.
Using the method populate can be more efficient than using the version of the execute method that takes no parameters because it does not open a new connection and re-execute this CachedRowSet object's command. Using the populate method is more a matter of convenience when compared to using the version of execute that takes a ResultSet object. This method should close any database connections that it creates to ensure that this CachedRowSet object is disconnected except when it is reading data from its data source or writing data to its data source.
The reader for this CachedRowSet object will use conn to establish a connection to the data source so that it can execute the rowset's command and read data from the the resulting ResultSet object into this CachedRowSet object. This method also closes conn after it has populated this CachedRowSet object.
If this method is called when an implementation has already been populated, the contents and the metadata are re set. Also, if this method is called before the method acceptChanges has been called to commit outstanding updates, those updates are lost. Parameters: conn - a standard JDBC Connection object with valid properties Throws: SQLException - if an invalid Connection object is supplied or an error occurs in establishing the connection to the data source See Also: populate java.
This method calls on this CachedRowSet object's writer to do the work behind the scenes. The writer will attempt to propagate changes made in this CachedRowSet object back to the data source. When the method acceptChanges executes successfully, in addition to writing changes to the data source, it makes the values in the current row be the values in the original row.
Depending on the synchronization level of the SyncProvider implementation being used, the writer will compare the original values with those in the data source to check for conflicts.
When there is a conflict, the RIOptimisticProvider implementation, for example, throws a SyncProviderException and does not write anything to the data source. An application may choose to catch the SyncProviderException object and retrieve the SyncResolver object it contains.
The SyncResolver object lists the conflicts row by row and sets a lock on the data source to avoid further conflicts while the current conflicts are being resolved. Further, for each conflict, it provides methods for examining the conflict and setting the value that should be persisted in the data source. After all conflicts have been resolved, an application must call the acceptChanges method again to write resolved values to the data source.
If all of the values in the data source are already the values to be persisted, the method acceptChanges does nothing. Some provider implementations may use locks to ensure that there are no conflicts. In such cases, it is guaranteed that the writer will succeed in writing changes to the data source when the method acceptChanges is called.
Why must it be a stream resultset? Is this advice helpful? Usually, there's one topic in an issue. It's also OK that we talk about only one case at a time without any others in this issue. I'll create a todo list to be resolved one by one. Thanks tuohai ,. Sorry I had to clarify earlier about this. Now only remains cases c and d. Will you create topics on how to fix cases c and d mentioned above? Or should I create two other topics for the issues of c and d.
These two cases may be bugs though. Fow case c and d, can you please create two separate issues? Because bug report is needed, I can't do that instead of you. I'd like to ask some questions before the issues are created, therefore you can answer there. It seems like client behavior. Just like we met before. Meanwhile, does it work when your client connect directly to a PostgreSQL server?
You are indeed right. These are client behaviours and nothing to do with the Sharding Proxy. I think it is kind of important because in many cases you want the resultset to be disconnected from the datasource and CachedRowSet is a good option for this. Thanks again for your help and support. I think this issue thread can be close now. I did put it in sharding-proxy about two years ago at the beginning of the sharding-proxy development. But not for long, our team find there's side-effect.
I can't remeber the details of what the side-effect it is, but I can make sure we can't use it anymore from then. So, there's no plan to enable the CachedRowSet mechanism for the moment. But don't worry, maybe you are right, we can restart the discussion about it if you want.
You can create an issue about it anytime. Skip to content. Star New issue. Jump to bottom. Labels type: question. Linked pull requests. Copy link. Hi, Apparently, when I get the returned resultset from the sharding-proxy, I can only scroll forward to get the rows. Thanks, Parsa. Fill in the bug report will help. Bug Report For English only , other languages will not accept.
Before report a bug, make sure you have: Searched open and closed GitHub issues. Read documentation: ShardingSphere Doc. Please answer these questions before submitting your issue. Which version of ShardingSphere did you use?
What part of their respective Javadoc didn't you understand? Add a comment. Active Oldest Votes. Improve this answer. Basil Bourque k 75 75 gold badges silver badges bronze badges.
Vivek Kumar Vivek Kumar 5 5 silver badges 16 16 bronze badges. Thanks you Vivek kumar. More info: You will need to find an implementation of these RowSet interfaces. Sun provided an open-source implementation. You may find others too. RowSet interface also provides methods for setting input parameters to this SQL query. After the required input parameters are set, the SQL query can be processed to populate the RowSet object with data from the underlying data source. The following code illustrates this simple sequence:.
In the preceding example, the employee number is set as the input or bind parameter for the SQL query specified in the command property of the RowSet object. When the SQL query is processed, the RowSet object is filled with the employee name and salary information of the employee whose employee number is RowSet interface extends the java.
ResultSet interface. The RowSet interface, therefore, provides cursor movement and positioning methods, which are inherited from the ResulSet interface, for traversing through data in a RowSet object.
Some of the inherited methods are absolute , beforeFirst , afterLast , next , and previous. The RowSet interface can be used just like a ResultSet interface for retrieving and updating data.
The RowSet interface provides an optional way to implement a scrollable and updatable result set. All the fields and methods provided by the ResultSet interface are implemented in RowSet. In the preceding code, the cursor position is initialized to the position before the first row of the RowSet by the beforeFirst method.
The rows are retrieved in forward direction using the next method. In the preceding code, the cursor position is initialized to the position after the last row of the RowSet. The rows are retrieved in reverse direction using the previous method of RowSet. Inserting, updating, and deleting rows are supported by the RowSet feature as they are in the ResultSet feature. In order to make the RowSet updatable, you must call the setReadOnly false and acceptChanges methods.
In the preceding code, a call to the absolute method with a parameter 5 takes the cursor to the fifth position of the RowSet and a call to the moveToInsertRow method creates a place for the insertion of a new row into the RowSet. The update XXX methods are used to update the newly created row. When all the columns of the row are updated, the insertRow is called to update the RowSet.
The changes are committed through acceptChanges method. A CachedRowSet is a RowSet in which the rows are cached and the RowSet is disconnected, that is, it does not maintain an active connection to the database. The oracle. It can interoperate with the reference implementation of Sun Microsystems. The OracleCachedRowSet class in the ojdbc The RowSet object is populated using the execute method.
After the execute method has been processed, the RowSet object can be used as a java. ResultSet object to retrieve, scroll, insert, delete, or update data. You can also set the connection type, but it is optional.
Call the execute method to populate the CachedRowSet object. Calling execute runs the query set as a property on this RowSet. To do so, complete the following steps:.
Pass the already available ResultSet object to the populate method to populate the RowSet object. In the preceding example, a ResultSet object is obtained by running a query and the retrieved ResultSet object is passed to the populate method of the CachedRowSet object to populate the contents of the result set into the CachedRowSet.
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