Ubuntu Manpage: tdbc::connection - TDBC connection object

NAME

       tdbc::connection - TDBC connection object

SYNOPSIS

       package require tdbc 1.0
       package require tdbc::driver version

       tdbc::driver::connection create db ?-option value...?

       db configure ?-option value...?
       db close
       db foreignkeys ?-primary tableName? ?-foreign tableName?
       db prepare sql-code
       db preparecall call
       db primarykeys tableName
       db statements
       db resultsets
       db tables ?pattern?
       db columns table ?pattern?
       db begintransaction
       db commit
       db rollback
       db transaction script
       db allrows ?-as lists|dicts? ?-columnsvariable name? ?--? sql-code ?dictionary?
       db foreach ?-as lists|dicts? ?-columnsvariable name? ?--? varName sqlcode ?dictionary?
              script
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DESCRIPTION

Every database driver for TDBC (Tcl DataBase Connectivity) implements a connection object
that represents a connection to a database. By convention, this object is created by the
command, tdbc::driver::connection create. This command accepts the name of a Tcl command
that will represent the connection and a possible set of options (see CONFIGURATION
OPTIONS). It establishes a connection to the database and returns the name of the newly-
created Tcl command.

The configure object command on a database connection, if presented with no arguments,
returns a list of alternating keywords and values representing the connection's current
configuration. If presented with a single argument -option, it returns the configured
value of the given option. Otherwise, it must be given an even number of arguments which
are alternating options and values. The specified options receive the specified values,
and nothing is returned.

The close object command on a database connection closes the connection. All active
statements and result sets on the connection are closed. Any uncommitted transaction is
rolled back. The object command is deleted.

The prepare object command on a database connection prepares a SQL statement for
execution. The sql-code argument must contain a single SQL statement to be executed. Bound
variables may be included. The return value is a newly-created Tcl command that represents
the statement. See tdbc::statement for more detailed discussion of the SQL accepted by the
prepare object command and the interface accepted by a statement.

On a database connection where the underlying database and driver support stored
procedures, the preparecall object command prepares a call to a stored procedure for
execution. The syntax of the stored procedure call is:

?resultvar =? procname(?arg ?, arg...?)

The return value is a newly-created Tcl command that represents the statement. See
tdbc::statement for the interface accepted by a statement.

The statements object command returns a list of statements that have been created by
prepare and preparecall statements against the given connection and have not yet been
closed.

The resultsets object command returns a list of result sets that have been obtained by
executing statements prepared using the given connection and not yet closed.

The tables object command allows the program to query the connection for the names of
tables that exist in the database. The optional pattern parameter is a pattern to match
the name of a table. It may contain the SQL wild-card characters '%' and ´_´. The return
value is a dictionary whose keys are table names and whose values are subdictionaries. See
the documentation for the individual database driver for the interpretation of the values.

The columns object command allows the program to query the connection for the names of
columns that exist in a given table. The optional pattern parameter is a pattern to match
the name of a column. It may contain the SQL wild-card characters '%' and ´_´. The return
value is a dictionary whose keys are column names and whose values are dictionaries. Each
of the subdictionaries will contain at least the following keys and values (and may
contain others whose usage is determined by a specific database driver).

type Contains the data type of the column, and will generally be chosen from the set,
bigint, binary, bit, char, date, decimal, double, float, integer, longvarbinary,
longvarchar, numeric, real, time, timestamp, smallint, tinyint, varbinary, and
varchar. (If the column has a type that cannot be represented as one of the above,
type will contain a driver-dependent description of the type.)

precision
Contains the precision of the column in bits, decimal digits, or the width in
characters, according to the type.

scale Contains the scale of the column (the number of digits after the radix point), for
types that support the concept.

nullable
Contains 1 if the column can contain NULL values, and 0 otherwise.

The primarykeys object command allows the program to query the connection for the primary
keys belonging to a given table. The tableName parameter identifies the table being
interrogated. The result is a list of dictionaries enumerating the keys (in a similar
format to the list returned by $connection allrows -as dicts). The keys of the dictionary
may include at least the following. Values that are NULL or meaningless in a given
database are omitted.

tableCatalog
Name of the catalog in which the table appears.

tableSchema
Name of the schema in which the table appears.

tableName
Name of the table owning the primary key.

constraintCatalog
Name of the catalog in which the primary key constraint appears. In some database
systems, this may not be the same as the table's catalog.

constraintSchema
Name of the schema in which the primary key constraint appears. In some database
systems, this may not be the same as the table's schema.

constraintName
Name of the primary key constraint,

columnName
Name of a column that is a member of the primary key.

ordinalPosition
Ordinal position of the column within the primary key.

To these columns may be added additional ones that are specific to a particular database
system.

The foreignkeys object command allows the program to query the connection for foreign key
relationships that apply to a particular table. The relationships may be constrained to
the keys that appear in a particular table (-foreign tableName), the keys that refer to a
particular table (-primary tableName), or both. At least one of -primary and -foreign
should be specified, although some drivers will enumerate all foreign keys in the current
catalog if both options are omitted. The result of the foreignkeys object command is a
list of dictionaries, with one list element per key (in a similar format to the list
returned by $connection allrows -as dicts). The keys of the dictionary may include at
least the following. Values that are NULL or meaningless in a given database are omitted.

foreignConstraintCatalog
Catalog in which the foreign key constraint appears.

foreignConstraintSchema
Schema in which the foreign key constraint appears.

foreignConstraintName
Name of the foreign key constraint.

primaryConstraintCatalog
Catalog holding the primary key constraint (or unique key constraint) on the column
to which the foreign key refers.

primaryConstraintSchema
Schema holding the primary key constraint (or unique key constraint) on the column
to which the foreign key refers.

primaryConstraintName
Name of the primary key constraint (or unique key constraint) on the column to
which the foreign key refers.

updateAction
Action to take when an UPDATE statement invalidates the constraint. The value will
be CASCADE, SET DEFAULT, SET NULL, RESTRICT, or NO ACTION.

deleteAction
Action to take when a DELETE statement invalidates the constraint. The value will
be CASCADE, SET DEFAULT, SET NULL, RESTRICT, or NO ACTION.

primaryCatalog
Catalog name in which the primary table (the one to which the foreign key refers)
appears.

primarySchema
Schema name in which the primary table (the one to which the foreign key refers)
appears.

primaryTable
Table name of the primary table (the one to which the foreign key refers).

primaryColumn
Name of the column to which the foreign key refers.

foreignCatalog
Name of the catalog in which the table containing the foreign key appears.

foreignSchema
Name of the schema in which the table containing the foreign key appears.

foreignTable
Name of the table containing the foreign key.

foreignColumn
Name of the column appearing in the foreign key.

ordinalPosition
Position of the column in the foreign key, if the key is a compound key.

The begintransaction object command on a database connection begins a transaction on the
database. If the underlying database does not support atomic, consistent, isolated,
durable transactions, the begintransaction object command returns an error reporting the
fact. Similarly, if multiple begintransaction commands are executed withough an
intervening commit or rollback command, an error is returned unless the underlying
database supports nested transactions.

The commit object command on a database connection ends the most recent transaction
started by begintransaction and commits changes to the database.

The rollback object command on a database connection rolls back the most recent
transaction started by begintransaction. The state of the database is as if nothing
happened during the transaction.

The transaction object command on a database connection presents a simple way of bundling
a database transaction. It begins a transaction, and evaluates the supplied script
argument as a Tcl script in the caller's scope. If script terminates normally, or by
break, continue, or return, the transaction is committed (and any action requested by
break, continue, or return takes place). If the commit fails for any reason, the error in
the commit is treated as an error in the script. In the case of an error in script or in
the commit, the transaction is rolled back and the error is rethrown. Any nonstandard
return code from the script causes the transaction to be rolled back and then is rethrown.

The allrows object command prepares a SQL statement (given by the sql-code parameter) to
execute against the database. It then executes it (see tdbc::statement for details) with
the optional dictionary parameter giving bind variables. Finally, it uses the allrows
object command on the result set (see tdbc::resultset) to construct a list of the results.
Finally, both result set and statement are closed. The return value is the list of
results.

The foreach object command prepares a SQL statement (given by the sql-code parameter) to
execute against the database. It then executes it (see tdbc::statement for details) with
the optional dictionary parameter giving bind variables. Finally, it uses the foreach
object command on the result set (see tdbc::resultset) to evaluate the given script for
each row of the results. Finally, both result set and statement are closed, even if the
given script results in a return, an error, or an unusual return code.

CONFIGURATION OPTIONS

The configuration options accepted when the connection is created and on the connection's
configure object command include the following, and may include others specific to a
database driver.

-encoding name
Specifies the encoding to be used in connecting to the database. The name should
be one of the names accepted by the encoding command. This option is usually
unnecessary; most database drivers can figure out the encoding in use by
themselves.

-isolation level
Specifies the transaction isolation level needed for transactions on the database.
The acceptable values for level are shown under TRANSACTION ISOLATION LEVELS.

-timeout ms
Specifies the maximum time to wait for a an operation database engine before
reporting an error to the caller. The ms argument gives the maximum time in
milliseconds. A value of zero (the default) specifies that the calling process is
to wait indefinitely for database operations.

-readonly flag
Specifies that the connection will not modify the database (if the Boolean
parameter flag is true), or that it may modify the database (if flag is false). If
flag is true, this option may have the effect of raising the transaction isolation
level to readonly.

TRANSACTION ISOLATION LEVELS
The acceptable values for the -isolation configuration option are as follows:

readuncommitted
Allows the transaction to read "dirty", that is, uncommitted data. This isolation
level may compromise data integrity, does not guarantee that foreign keys or
uniqueness constraints are satisfied, and in general does not guarantee data
consistency.

readcommitted
Forbids the transaction from reading "dirty" data, but does not guarantee
repeatable reads; if a transaction reads a row of a database at a given time, there
is no guarantee that the same row will be available at a later time in the same
transaction.

repeatableread
Guarantees that any row of the database, once read, will have the same values for
the life of a transaction. Still permits "phantom reads" (that is, newly-added rows
appearing if a table is queried a second time).

serializable
The most restrictive (and most expensive) level of transaction isolation. Any query
to the database, if repeated, will return precisely the same results for the life
of the transaction, exactly as if the transaction is the only user of the database.

readonly
Behaves like serializable in that the only results visible to the transaction are
those that were committed prior to the start of the transaction, but forbids the
transaction from modifying the database.

A database that does not implement one of these isolation levels will instead use the next
more restrictive isolation level. If the given level of isolation cannot be obtained, the
database interface throws an error reporting the fact. The default isolation level is
readcommitted.

A script should not the isolation level when a transaction is in progress.

KEYWORDS

       TDBC, SQL, database, connectivity, connection, resultset, statement

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