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## edu.udo.cs.miningmart.db
Class DbCore

    java.lang.Object
      edu.udo.cs.miningmart.db.DbCore

Direct Known Subclasses:
  DbCoreOracle, DbCorePostgres

public abstract class DbCore
extends java.lang.Object

Abstract superclass class to encapsulate most of the directly database related information. Subclasses realise the access to different DBMS. The only class referencing subclasses of `DbCore` is `DB`. However, the class is public because it provides static methods to deal with different DBMS systems.

Version:
  $Id: DbCore.java,v 1.6 2006/04/11 14:10:16 euler Exp $
Author:
  Martin Scholz

Field Summary
`static java.lang.String` | `DBMS_ORACLE` Public constant to refer to the Database Management System (DBMS) Oracle.
`static java.lang.String` | `DBMS_POSTGRES` Public constant to refer to the Database Management System (DBMS) PostgreSQL.

Constructor Summary
`DbCore(java.lang.String url, java.lang.String dbName, java.lang.String user, java.lang.String passwd, M4InterfaceContext cal, boolean refersToM4Schema)` The constructor of this class establishes a new database connection.

Method Summary
`void` | `commitTransactions()` Commit the last transactions in the M4 database.
`void` | `createSQLFunction(java.lang.String myFunction)` Create a function in the database by using the given function definition.
`java.lang.String` | `createSqlIndex(java.lang.String tableName, java.lang.String[] attributes)` Creates a database index for the given table and set of attributes.
`void` | `createSQLView(Columnset cs, boolean materialize)` Create the generated sql definition for a new view within the database, or materialize the view as a table, if this is preferrable.
`abstract boolean` | `dropRelation(java.lang.String tableName)` Try to drop the table or view with the given name, if it exists.
`void` | `executeDBProcedure(java.lang.String procedureName, java.lang.String[] parameters)` Method to execute a stored procedure residing in the according schema.
`java.lang.String` | `executeSingleValueSqlRead(java.lang.String query)`
`java.lang.Long` | `executeSingleValueSqlReadL(java.lang.String query)`
`protected java.lang.Long` | `executeSingleValueSqlReadL(java.lang.String query, java.sql.Statement stmt)`
`java.sql.ResultSet` | `executeSqlRead(java.lang.String query)` Method to comfortably read from the database.
`void` | `executeSqlWrite(java.lang.String query)` Method to comfortably write to the database.
`void` | `finalize()` Closes the database connections.
`static java.lang.String` | `findDBMS(java.lang.String url)` Use this method to decide about the Database Management System (DBMS) which is to be used.
`abstract java.lang.String` | `getAttributeForColumnNames()` Abstract method to be implemented by the subclasses.
`abstract java.lang.String` | `getAttributeForColumnTypes()` Abstract method to be implemented by the subclasses.
`Print` | `getCasePrintObject()`
`abstract java.lang.String` | `getDatatypeName(java.lang.String m4RelDatatypeName, int size)` This method returns the DBMS-dependent name of the datatype which the current DBMS uses to realize the given M4-Relational Datatype.
`abstract short` | `getDbms()` Indicates the DBMS used.
`abstract java.lang.String` | `getM4DatatypeName(java.lang.String dbmsDatatypeName)` This method returns the M4-Relational Datatype that corresponds to the given DBMS-dependent name of a datatype.
`protected abstract long` | `getNextM4SequenceValue(java.sql.Statement stmt)`
`abstract java.util.Collection` | `getPrimaryKeyColumnNames(java.lang.String dbObjectName)` Returns a Collection with the names of the DB columns that belong to the given table or view and form its primary key, if such a key is declared by SQL constraints in the DB.
`abstract java.lang.String` | `getSelectStringAllColumnsForDbObject(java.lang.String dbObjectName)` Abstract method to be implemented by the subclasses.
`abstract java.lang.String` | `getSelectStringAllTables()` Abstract method to be implemented by the subclasses.
`abstract java.lang.String` | `getSelectStringAllViews()` Abstract method to be implemented by the subclasses.
`abstract java.lang.String` | `getSelectStringColumnDataTypes(java.lang.String dbObjectName, java.lang.String owner, java.lang.String columnName)` This method returns the DBMS-dependent SQL command that returns the name of the datatype of the given column in the given table or view (which is owned by the given owner).
`abstract java.lang.String` | `getTableOrViewType(java.lang.String dbObjectName)` Returns one of the TYPE_... constants in the class edu.udo.cs.miningmart.m4.Columnset, or null if the given String is neither a table or view.
`abstract java.util.Map` | `getTablesReferencedBy(java.lang.String dbObjectName)` Returns a Map that maps every column of the given table to the name of the table that it references as a foreign key, or to null if the column does not act as a foreign key.
`abstract java.lang.String` | `getTestQuery()`
`abstract java.lang.String` | `getUniqueRowIdentifier()` Abstract method to be implemented by the subclasses.
`boolean` | `hasOnlyForeignKeyColumns(java.lang.String dbObjectName)` Returns TRUE iff the given table/view has ONLY columns that act as foreign keys to other tables.
`protected abstract void` | `registerJDBC_Driver()` This method must be implemented by subclasses in order to use other JDBC drivers (for other DBMS, for example).
`void` | `rollback()` Roll back the last transactions (since the last commit) in the database.
`protected abstract void` | `switchAutocommitOff(java.sql.Connection con)` Since the transaction mechanism may be different for different DBMS, use this method to implement the Autocommit handling.
`abstract boolean` | `tableExists(java.lang.String tableName)` Returns TRUE if a table (not a view) with the given name exists in the database.

Methods inherited from class java.lang.Object
`clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### DBMS_ORACLE

    public static java.lang.String DBMS_ORACLE

  Public constant to refer to the Database Management System (DBMS) Oracle.

### DBMS_POSTGRES

    public static java.lang.String DBMS_POSTGRES

  Public constant to refer to the Database Management System (DBMS) PostgreSQL.

Constructor Detail

### DbCore

    public DbCore(java.lang.String url,
                  java.lang.String dbName,
                  java.lang.String user,
                  java.lang.String passwd,
                  M4InterfaceContext cal,
                  boolean refersToM4Schema)
           throws java.sql.SQLException

  The constructor of this class establishes a new database connection. Autocommit is set to false, so transaction management must be done individually by the database functions.

Parameters:
  `url` - Prefix of the database url
  `dbName` - name of the database
  `user` - name of the database user
  `passwd` - password for the database user
  `cal` - the `CompilerAccessLogic` of the current thread. It is just needed in order to reach the appropriate `Print`-object for writing debug messages
  `refersToM4Schema` - is `true` iff the connection refers to the M4 schema. Useful to decide whether triggers need to be switched off etc.
Throws:
  `java.sql.SQLException`

Method Detail

### findDBMS

    public static java.lang.String findDBMS(java.lang.String url)

  Use this method to decide about the Database Management System (DBMS) which is to be used. This method is given the DB connection URL (consisting of driver and location) and returns one of the public constants of this class whose name starts with "DBMS_". Currently, this method uses the driver name to decide about the DBMS.

  Parameters:
    `url` - The DB connection URL
  Returns:
    One of the public String constants of this class.

### getCasePrintObject

    public Print getCasePrintObject()

### finalize

    public void finalize()
                  throws java.sql.SQLException

  Closes the database connections. If the database is no longer used this Finalization method closes the database connection. Currently, I guess a java exit is an acceptable disconnect as well. If not we have to register a addShutdownHook in Class Runtime

  Throws:
    `java.sql.SQLException`

### getDbms

    public abstract short getDbms()

  Indicates the DBMS used.

### registerJDBC_Driver

    protected abstract void registerJDBC_Driver()
                                         throws java.sql.SQLException

  This method must be implemented by subclasses in order to use other JDBC drivers (for other DBMS, for example).

  Throws:
    `java.sql.SQLException`

### switchAutocommitOff

    protected abstract void switchAutocommitOff(java.sql.Connection con)
                                         throws java.sql.SQLException

  Since the transaction mechanism may be different for different DBMS, use this method to implement the Autocommit handling.

  Throws:
    `java.sql.SQLException`

### commitTransactions

    public void commitTransactions()
                            throws java.sql.SQLException

  Commit the last transactions in the M4 database.

  Throws:
    `java.sql.SQLException`

### rollback

    public void rollback()
                  throws java.sql.SQLException

  Roll back the last transactions (since the last commit) in the database.

  Throws:
    `java.sql.SQLException`

### executeSqlWrite

    public void executeSqlWrite(java.lang.String query)
                         throws java.sql.SQLException,
                                DbConnectionClosed

  Method to comfortably write to the database. If possible automatic batching is applied.

  Parameters:
    `query` - an SQL query to be executed. This has to be a write operation to the database, or an SQL string to execute a procedure in the according schema.
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### createSQLView

    public void createSQLView(Columnset cs,
                              boolean materialize)
                       throws java.sql.SQLException,
                              DbConnectionClosed

  Create the generated sql definition for a new view within the database, or materialize the view as a table, if this is preferrable.

  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### createSQLFunction

    public void createSQLFunction(java.lang.String myFunction)
                           throws java.sql.SQLException,
                                  DbConnectionClosed

  Create a function in the database by using the given function definition.

  Parameters:
    `myFunction` - a function definition for a SQL function
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### createSqlIndex

    public java.lang.String createSqlIndex(java.lang.String tableName,
                                           java.lang.String[] attributes)
                                    throws java.sql.SQLException,
                                           DbConnectionClosed

  Creates a database index for the given table and set of attributes.

  Parameters:
    `tableName` - the table to create an index on
    `attributes` - an array of attribute names, specifying for which attributes an index should be created
  Returns:
    the name of the index or `null`.
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### executeSqlRead

    public java.sql.ResultSet executeSqlRead(java.lang.String query)
                                      throws java.sql.SQLException,
                                             DbConnectionClosed

  Method to comfortably read from the database.

  Parameters:
    `query` - an SQL query to be executed. This has to be a read operation on the database.
  Returns:
    the corresponding `ResultSet`
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### executeSingleValueSqlReadL

    protected java.lang.Long executeSingleValueSqlReadL(java.lang.String query,
                                                        java.sql.Statement stmt)
                                                 throws java.sql.SQLException

  Parameters:
    `query` - an SQL query to be executed. This has to be a read operation yielding a single (numeric) value, which is convertable to datatype long.
    `stmt` - the `Statement` to be used to execute the query
  Returns:
    the result as a `String`, or `null`, if no value was returned.
  Throws:
    `java.sql.SQLException`

### executeSingleValueSqlReadL

    public java.lang.Long executeSingleValueSqlReadL(java.lang.String query)
                                              throws java.sql.SQLException,
                                                     DbConnectionClosed

  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`
  See Also:
    `In contrast to that method, this method creates and then closes its own `Statement`.`

### executeSingleValueSqlRead

    public java.lang.String executeSingleValueSqlRead(java.lang.String query)
                                               throws java.sql.SQLException,
                                                      DbConnectionClosed

  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`
  See Also:
    `In contrast to that method, this method creates and then closes its own `Statement`.`

### getNextM4SequenceValue

    protected abstract long getNextM4SequenceValue(java.sql.Statement stmt)
                                            throws M4Exception

  Parameters:
    `stmt` - the `Statement` to be used to execute the query
  Returns:
    the value returned by the sequence (installed in the M4 schema).
  Throws:
    `M4Exception` - if for some reason the sequence does not return a value

### executeDBProcedure

    public void executeDBProcedure(java.lang.String procedureName,
                                   java.lang.String[] parameters)
                            throws java.sql.SQLException,
                                   DbConnectionClosed,
                                   M4CompilerError

  Method to execute a stored procedure residing in the according schema.

  Parameters:
    `procedureName` - the name of the stored procedure in the database
    `parameters` - the parameters to be passed to the stored procedure. In SQL code these parameters are comma separated.
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`
    `M4CompilerError`

### getSelectStringAllTables

    public abstract java.lang.String getSelectStringAllTables()

  Abstract method to be implemented by the subclasses. Returns an SQL String that selects the names of all tables from the current schema. This is DBMS-dependent.

  Returns:
    An SQL String

### getSelectStringAllViews

    public abstract java.lang.String getSelectStringAllViews()

  Abstract method to be implemented by the subclasses. Returns an SQL String that selects the names of all views from the current schema. This is DBMS-dependent.

  Returns:
    An SQL String

### tableExists

    public abstract boolean tableExists(java.lang.String tableName)
                                 throws M4Exception

  Returns TRUE if a table (not a view) with the given name exists in the database.

  Parameters:
    `tableName` - the table name
  Returns:
    TRUE or FALSE
  Throws:
    `M4Exception`

### getSelectStringAllColumnsForDbObject

    public abstract java.lang.String getSelectStringAllColumnsForDbObject(java.lang.String dbObjectName)

  Abstract method to be implemented by the subclasses. Returns the SQL String that selects all column names and types for the given Table or View name from the business data schema. This is DBMS-dependent.

  Parameters:
    `dbObjectName` - Name of a table or view in the business data schema
  Returns:
    An SQL String

### getAttributeForColumnNames

    public abstract java.lang.String getAttributeForColumnNames()

  Abstract method to be implemented by the subclasses. Returns the name of the column that contains the column names. This is DBMS-dependent.

  Returns:
    the name of the column that contains the column names.

### getAttributeForColumnTypes

    public abstract java.lang.String getAttributeForColumnTypes()

  Abstract method to be implemented by the subclasses. Returns the name of the column that contains the column types. This is DBMS-dependent.

  Returns:
    the name of the column that contains the column types.

### getUniqueRowIdentifier

    public abstract java.lang.String getUniqueRowIdentifier()

  Abstract method to be implemented by the subclasses. Returns a String that can be used to uniquely identify table rows in SQL-Statements. This is DBMS-dependent.

  Returns:
    the unique row identifier name

### getTablesReferencedBy

    public abstract java.util.Map getTablesReferencedBy(java.lang.String dbObjectName)
                                                 throws java.sql.SQLException,
                                                        DbConnectionClosed

  Returns a Map that maps every column of the given table to the name of the table that it references as a foreign key, or to null if the column does not act as a foreign key. The Map uses only Strings.

  Parameters:
    `dbObjectName` - the given table name
  Returns:
    a Map whose keys and values are Strings
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### hasOnlyForeignKeyColumns

    public boolean hasOnlyForeignKeyColumns(java.lang.String dbObjectName)
                                     throws java.sql.SQLException,
                                            DbConnectionClosed

  Returns TRUE iff the given table/view has ONLY columns that act as foreign keys to other tables.

  Parameters:
    `dbObjectName` - name of given table/view
  Returns:
    a boolean value
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### getPrimaryKeyColumnNames

    public abstract java.util.Collection getPrimaryKeyColumnNames(java.lang.String dbObjectName)
                                                           throws java.sql.SQLException,
                                                                  DbConnectionClosed

  Returns a Collection with the names of the DB columns that belong to the given table or view and form its primary key, if such a key is declared by SQL constraints in the DB. Otherwise null is returned.

  Parameters:
    `dbObjectName` - the name of the given table or view
  Returns:
    a Collection of Strings
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### getTableOrViewType

    public abstract java.lang.String getTableOrViewType(java.lang.String dbObjectName)
                                                 throws java.sql.SQLException,
                                                        DbConnectionClosed

  Returns one of the TYPE_... constants in the class edu.udo.cs.miningmart.m4.Columnset, or null if the given String is neither a table or view.

  Parameters:
    `dbObjectName` - name of a table or view
  Returns:
    a String with the type information
  Throws:
    `java.sql.SQLException`
    `DbConnectionClosed`

### getDatatypeName

    public abstract java.lang.String getDatatypeName(java.lang.String m4RelDatatypeName,
                                                     int size)

  This method returns the DBMS-dependent name of the datatype which the current DBMS uses to realize the given M4-Relational Datatype.

  Parameters:
    `m4RelDatatypeName` - name of the M4 Relational Datatype
    `size` - A size to be returned with the datatype, if the DBMS allows that. For example, if the M4 Relational Datatype is NUMBER and length is 10, then the return value will be the String "NUMBER(10)" if the DBMS is Oracle. If this length is not positive, the datatype will be returned without a size, in the example: "NUMBER". The DBMS may not allow lengths at all, in which case also the datatype without a size is returned.
  Returns:
    A DBMS-dependent string that contains a datatype name.

### getM4DatatypeName

    public abstract java.lang.String getM4DatatypeName(java.lang.String dbmsDatatypeName)

  This method returns the M4-Relational Datatype that corresponds to the given DBMS-dependent name of a datatype.

  Parameters:
    `dbmsDatatypeName` - the name of the datatype in the underlying DBMS
  Returns:
    the corresponding M4 Relational Datatype

### getSelectStringColumnDataTypes

    public abstract java.lang.String getSelectStringColumnDataTypes(java.lang.String dbObjectName,
                                                                    java.lang.String owner,
                                                                    java.lang.String columnName)

  This method returns the DBMS-dependent SQL command that returns the name of the datatype of the given column in the given table or view (which is owned by the given owner).

  Parameters:
    `dbObjectName` - Name of a table or view in the business data schema
    `owner` - Name of the owner of the table or view
    `columnName` - Name of the column whose datatype is returned
  Returns:
    the DBMS-dependent name of the datatype of the column with the given name

### dropRelation

    public abstract boolean dropRelation(java.lang.String tableName)
                                  throws M4Exception

  Try to drop the table or view with the given name, if it exists. Returns TRUE iff the table had existed, FALSE otherwise.

  Parameters:
    `tableName` - the name of the table to be dropped
  Returns:
    TRUE iff the table had existed before it was removed, FALSE if nothing was done.
  Throws:
    `M4Exception`

### getTestQuery

    public abstract java.lang.String getTestQuery()

  Returns:
    a `String` that can be used as a query to test the DB connection.

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