org.tentackle.persist

Class Query

java.lang.Object

org.tentackle.persist.Query

public class Query
extends Object

A database query.

Combines the generation of an sql-string and parameter set for the ResultSetWrapper. Useful for one-time queries entered by the user.
Notice that by default the underlying prepared statement is closed when the resultset (or cursor) is closed by the application. You can change that behaviour, however.

Notice further, that the columns returned by the select must be provided by the application via add() _before_ execution. The SELECT, however, and LIMIT/OFFSET clauses are provided by the query automatically, because they are backend-specific.

Author:

harald

Constructor Summary

Constructors

Constructor and Description
Query() Creates a query.

Method Summary

Modifier and Type	Method and Description
void	add(String sql, Object... data) Appends an sql-part and corresponding parameters to this query.
void	apply(Db db, PreparedStatementWrapper st) Applies the query parameters to the statement. Optionally applies limit, offset as well.
int	applyParameters(PreparedStatementWrapper st, int ndx) Apply the query parameters only.
StringBuilder	buildInnerSql() Builds the inner sql query string.
String	createSql(Db db) Creates the SQL-String of this query. Optionally modifies the sql query according to limit and offset.
StatementKey	createStatementKey(String sql) Creates the statement key.
ResultSetWrapper	execute(Db db) Executes the query with ResultSet.TYPE_FORWARD_ONLY and ResultSet.CONCUR_READ_ONLY.
ResultSetWrapper	execute(Db db, int resultSetType) Executes the query with ResultSet.CONCUR_READ_ONLY.
ResultSetWrapper	execute(Db db, int resultSetType, int resultSetConcurrency) Executes the query.
int	getFetchSize() Gets the fetchsize.
int	getLimit() Gets the maximum number of rows for this query.
int	getMaxRows() Gets the maximum row count for this cursor
int	getOffset() Gets the offset of this query.
int	getRowCount(Db db) Gets the number of objects returned by this query.
boolean	isStatementCached() Returns whether statement caching is enabled.
void	setFetchSize(int fetchSize) Sets the optional fetchsize.
void	setLimit(int limit) Sets the maximum number of rows to retrieve for this query.
void	setMaxRows(int maxRows) Sets the optional maximum row count for this cursor.
void	setOffset(int offset) Sets an offset, i.e.
void	setStatementCached(boolean statementCached) Enables caching of the prepared statement. By default, queries are one-time prepared statements that will be closed when the resultset is closed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Query

public Query()

Creates a query.

Method Detail

setStatementCached

public void setStatementCached(boolean statementCached)

Enables caching of the prepared statement.
By default, queries are one-time prepared statements that will be closed when the resultset is closed. However, if a query uses a fixed SQL string and is executed a significant number of times, the prepared statement can be prepared only once and re-used afterwards. Please notice, that once prepared with caching, the statement will remain open until it is closed explicitly.

Parameters:

statementCached - true if prepare only once and reuse cached statement, false if one-shot

isStatementCached

public boolean isStatementCached()

Returns whether statement caching is enabled.

Returns:

true if prepare only once and reuse cached statement, false if one-shot (default)

setOffset

public void setOffset(int offset)

Sets an offset, i.e. number of rows to skip in a query. By default the offset is 0.

Parameters:

offset - the offset, 0 to disable

getOffset

public int getOffset()

Gets the offset of this query.

Returns:

the number of rows to skip, 0 if no offset

setLimit

public void setLimit(int limit)

Sets the maximum number of rows to retrieve for this query. e

Parameters:

limit - the maximum number of rows, 0 if ulimited (default)

getLimit

public int getLimit()

Gets the maximum number of rows for this query.

Returns:

the maximum number of rows, 0 if ulimited (default)

add

public void add(String sql,
                Object... data)

Appends an sql-part and corresponding parameters to this query.

 Example: add(" AND CN_ID=?", object.getId());
          add(" AND CN_MONEY=?", object.getAmount());
 

Parameters:

sql - is the SQL-string

data - is an array of parameters

setFetchSize

public void setFetchSize(int fetchSize)

Sets the optional fetchsize. 0 = drivers default.

Parameters:

fetchSize - the fetchsize

See Also:

ResultSetWrapper.setFetchSize(int)

getFetchSize

public int getFetchSize()

Gets the fetchsize.

Returns:

the fetchsize

See Also:

ResultSetWrapper.getFetchSize()

setMaxRows

public void setMaxRows(int maxRows)

Sets the optional maximum row count for this cursor.

Parameters:

maxRows - the max rows, 0 = no limit

getMaxRows

public int getMaxRows()

Gets the maximum row count for this cursor

Returns:

the max rows, 0 = no limit

execute

public ResultSetWrapper execute(Db db,
                                int resultSetType,
                                int resultSetConcurrency)

Executes the query.

Parameters:

db - is the database connection

resultSetType - is one of ResultSet.TYPE_...

resultSetConcurrency - is one of ResultSet.CONCUR_..

Returns:

the result set

execute

public ResultSetWrapper execute(Db db,
                                int resultSetType)

Executes the query with ResultSet.CONCUR_READ_ONLY.

Parameters:

db - is the database connection

resultSetType - is one of ResultSet.TYPE_...

Returns:

the result set

execute

public ResultSetWrapper execute(Db db)

Executes the query with ResultSet.TYPE_FORWARD_ONLY and ResultSet.CONCUR_READ_ONLY.

Parameters:

db - is the database connection

Returns:

the result set

getRowCount

public int getRowCount(Db db)

Gets the number of objects returned by this query.

This is not done by retrieving all rows but by a "SELECT COUNT(1)". Applications may use this in conjunction with limit and offset for pagination (in web pages, for example).

Parameters:

db - the db connection

Returns:

the number of rows for this query

apply

public void apply(Db db,
                  PreparedStatementWrapper st)

Applies the query parameters to the statement.
Optionally applies limit, offset as well.

Parameters:

db - the database connection

st - the prepared statement

applyParameters

public int applyParameters(PreparedStatementWrapper st,
                           int ndx)

Apply the query parameters only.

Parameters:

st - the statement

ndx - the starting index

Returns:

the next paramater index

createSql

public String createSql(Db db)

Creates the SQL-String of this query.
Optionally modifies the sql query according to limit and offset.

Parameters:

db - the db connection

Returns:

the sql string

createStatementKey

public StatementKey createStatementKey(String sql)

Creates the statement key.

Parameters:

sql - the SQL string sent to the backend

Returns:

the key

buildInnerSql

public StringBuilder buildInnerSql()

Builds the inner sql query string.

Returns:

the sql string