com.mckoi.database.interpret
Class Statement

java.lang.Object
  extended by com.mckoi.database.interpret.Statement
Direct Known Subclasses:
AlterTable, Call, Compact, CompleteTransaction, CreateTable, CreateTrigger, Delete, DropTable, DropTrigger, Function, Insert, Misc, NoOp, PrivManager, Schema, Select, Sequence, Set, Show, UpdateTable, UserManager, ViewManager

public abstract class Statement
extends java.lang.Object

Provides a set of useful utility functions to use by all the interpretted statements.

Author:
Tobias Downer

Field Summary
protected  StatementTree cmd
          The StatementTree object that is the container for the query.
protected  DatabaseConnection database
          The Database context.
protected  SQLQuery query
          The SQLQuery object that was used to produce this statement.
protected  java.util.Vector table_list
          The list of all FromTableInterface objects of resources referenced in this query.
protected  User user
          The user context.
 
Constructor Summary
Statement()
           
 
Method Summary
protected  void addTable(FromTableInterface table)
          Add an FromTableInterface that is used within this query.
 DebugLogger Debug()
          Returns a DebugLogger object used to log debug commands.
abstract  Table evaluate()
          Evaluates the statement and returns a table that represents the result set.
 void init(DatabaseConnection db, StatementTree stree, SQLQuery query)
          Sets up internal variables for this statement for derived classes to use.
abstract  void prepare()
          Prepares the statement with the given Database object.
 void resolveTree()
          Performs initial preparation on the contents of the StatementTree by resolving all sub queries and mapping functions to their executable forms.
 Variable resolveVariableName(Variable v)
          Given a Variable object, this will resolve the name into a column name the database understands (substitutes aliases, etc).
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

database

protected DatabaseConnection database
The Database context.


user

protected User user
The user context.


cmd

protected StatementTree cmd
The StatementTree object that is the container for the query.


query

protected SQLQuery query
The SQLQuery object that was used to produce this statement.


table_list

protected java.util.Vector table_list
The list of all FromTableInterface objects of resources referenced in this query. (FromTableInterface)

Constructor Detail

Statement

public Statement()
Method Detail

Debug

public final DebugLogger Debug()
Returns a DebugLogger object used to log debug commands.


resolveTree

public final void resolveTree()
                       throws DatabaseException
Performs initial preparation on the contents of the StatementTree by resolving all sub queries and mapping functions to their executable forms.

Given a StatementTree and a Database context, this method will convert all sub-queries found in the StatementTree to a Queriable object. In other words, all StatementTree are converted to Select objects. The given 'database' object is used as the session to prepare the sub-queries against.

This is called after 'init' and before 'prepare'.

Throws:
DatabaseException

resolveVariableName

public Variable resolveVariableName(Variable v)
Given a Variable object, this will resolve the name into a column name the database understands (substitutes aliases, etc).


addTable

protected void addTable(FromTableInterface table)
Add an FromTableInterface that is used within this query. These tables are used when we try to resolve a column name.


init

public final void init(DatabaseConnection db,
                       StatementTree stree,
                       SQLQuery query)
Sets up internal variables for this statement for derived classes to use. This is called before 'prepare' and 'isExclusive' is called.

It is assumed that any ? style parameters in the StatementTree will have been resolved previous to a call to this method.

Parameters:
db - the DatabaseConnection that will execute this statement.
stree - the StatementTree that contains the parsed content of the statement being executed.

prepare

public abstract void prepare()
                      throws DatabaseException
Prepares the statement with the given Database object. This is called before the statement is evaluated. The prepare statement queries the database and resolves information about the statement (for example, it resolves column names and aliases and determines the tables that are touched by this statement so we can lock the appropriate tables before we evaluate).

NOTE: Care must be taken to ensure that all methods called here are safe in as far as modifications to the data occuring. The rules for safety should be as follows. If the database is in EXCLUSIVE mode, then we need to wait until it's switched back to SHARED mode before this method is called. All collection of information done here should not involve any table state info. except for column count, column names, column types, etc. Queries such as obtaining the row count, selectable scheme information, and certainly 'getCellContents' must never be called during prepare. When prepare finishes, the affected tables are locked and the query is safe to 'evaluate' at which time table state is safe to inspect.

Throws:
DatabaseException

evaluate

public abstract Table evaluate()
                        throws DatabaseException,
                               TransactionException
Evaluates the statement and returns a table that represents the result set. This is called after 'prepare'.

Throws:
DatabaseException
TransactionException