DB::Object - SQL API


    use DB::Object;

    my $dbh = DB::Object->connect({
    driver => 'Pg',
    conf_file => 'db-settings.json',
    database => 'webstore',
    host => 'localhost',
    login => 'store-admin',
    schema => 'auth',
    debug => 3,
    }) || bailout( "Unable to connect to sql server on host localhost: ", DB::Object->error );
    # Legacy regular query
    my $sth = $dbh->prepare( "SELECT login,name FROM login WHERE login='jack'" ) ||
    die( $dbh->errstr() );
    $sth->execute() || die( $sth->errstr() );
    my $ref = $sth->fetchrow_hashref();
    # Get a list of databases;
    my @databases = $dbh->databases;
    # Doesn't exist? Create it:
    my $dbh2 = $dbh->create_db( 'webstore' );
    # Load some sql into it
    my $rv = $dbh2->do( $sql ) || die( $dbh->error );
    # Check a table exists
    $dbh->table_exists( 'customers' ) || die( "Cannot find the customers table!\n" );
    # Get list of tables, as array reference:
    my $tables = $dbh->tables;
    my $cust = $dbh->customers || die( "Cannot get customers object." );
    $cust->where( email => '' );
    my $str = $cust->delete->as_string;
    # Becomes: DELETE FROM customers WHERE email='john\'
    # Do some insert with transaction
    # Making some other inserts and updates here...
    my $cust_sth_ins = $cust->insert(
        first_name => 'Paul',
        last_name => 'Goldman',
        email => '',
        active => 0,
    ) || do
        # Rollback everything since the begin_work
        die( "Error while create query to add data to table customers: " . $cust->error );
    $result = $cust_sth_ins->as_string;
    # INSERT INTO customers (first_name, last_name, email, active) VALUES('Paul', 'Goldman', 'paul\', '0')
    ## Get the last used insert id
    my $id = $dbh->last_insert_id();
    $cust->where( email => '' );
    $cust->order( 'last_name' );
    $cust->having( email => qr/\@example/ );
    $cust->limit( 10 );
    my $cust_sth_sel = $cust->select || die( "An error occurred while creating a query to select data frm table customers: " . $cust->error );
    # Becomes:
    # SELECT id, first_name, last_name, email, created, modified, active, created::ABSTIME::INTEGER AS created_unixtime, modified::ABSTIME::INTEGER AS modified_unixtime, CONCAT(first_name, ' ', last_name) AS name FROM customers WHERE email='john\' HAVING email ~ '\@example' ORDER BY last_name LIMIT 10
    $cust->where( email => '' );
    my $cust_sth_upd = $cust->update( active => 0 )
    # Would become:
    # UPDATE ONLY customers SET active='0' WHERE email='john\'
    ## Lets' dump the result of our query
    ## First to STDERR
    $login->where( "login='jack'" );
    ## Now dump the result to a file
    $login->select->dump( "my_file.txt" );




DB::Object is a SQL API much alike DBI. So why use a private module instead of using that great DBI package?

At first, I started to inherit from DBI to conform to perlmod perl manual page and to general perl coding guidlines. It became very quickly a real hassle. Barely impossible to inherit, difficulty to handle error, too much dependent from an API that change its behaviour with new versions. In short, I wanted a better, more accurate control over the SQL connection.

So, DB::Object acts as a convenient, modifiable wrapper that provide the programmer with an intuitive, user-friendly and hassle free interface.



Create a new instance of DB::Object. Nothing much to say.


Create a new instance of DB::Object, but also attempts a conection to SQL server.

It can take either an array of value in the order database name, login, password, host, driver and optionally schema, or it can take a has or hash reference. The hash or hash reference attributes are as follow:

database or DB_NAME

The database name you wish to connect to

login or DB_LOGIN

The login used to access that database

passwd or DB_PASSWD

The password that goes along

host or DB_HOST

The server, that is hostname of the machine serving a SQL server.

port or DB_PORT

The port to connect to

driver or DB_DRIVER

The driver you want to use. It needs to be of the same type than the server you want to connect to. If you are connecting to a MySQL server, you would use mysql, if you would connecto to an Oracle server, you would use oracle.

You need to make sure that those driver are properly installed in the system before attempting to connect.

To install the required driver, you could start with the command line:

    perl -MCPAN -e shell

which will provide you a special shell to install modules in a convenient way.

schema or DB_SCHEMA

The schema to use to access the tables. Currently only used by PostgreSQL


This takes a hash reference and contains the standard DBI options such as PrintError, RaiseError, AutoCommit, etc

conf_file or DB_CON_FILE

This is used to specify a json connection configuration file. It can also provided via the environment variable DB_CON_FILE. It has the following structure:

    "database": "some_database",
    "host": "",
    "login": "sql_joe",
    "passwd": "some password",
    "driver": "Pg",
    "schema": "warehouse",
        "RaiseError": false,
        "PrintError": true,
        "AutoCommit": true

Alternatively, it can contain connections parameters for multiple databases and drivers, such as:

        "databases": [
            "database": "some_database",
            "host": "",
            "port": 5432,
            "login": "sql_joe",
            "passwd": "some password",
            "driver": "Pg",
            "schema": "warehouse",
                "RaiseError": false,
                "PrintError": true,
                "AutoCommit": true
            "database": "other_database",
            "host": "",
            "login": "sql_bob",
            "passwd": "other password",
            "driver": "mysql",
            "database": "/path/to/my/database.sqlite",
            "driver": "SQLite",
uri or DB_CON_URI

This is used to specify an uri to contain all the connection parameters for one database connection. It can also provided via the environment variable DB_CON_URI. For example:

Here the opt parameter is passed as a json string, for example:

    {"RaiseError": false, "PrintError":true, "AutoCommit":true}



Reset error message.

debug( [ 0 | 1 ] )

Toggle debug mode on/off

error( [ $string ] )

Get set error message. If an error message is provided, error will pass it to warn.

get( $parameter )

Get object parameter.

message( $string )

Provided a multi line string, message will display it on the STDERR if either verbose or debug mode is on.


Toggle verbose mode on/off

alias( %parameters )

Get/set alias for table fields in SELECT queries. The hash provided thus contain a list of field => alias pairs.


Return the sql query as a string.

avoid( [ @fields | \@fields ] )

Set the provided list of table fields to avoid when returning the query result. The list of fields can be provided either as an array of a reference to an array.

attribute( $name | %names )

Sets or get the value of database connection parameters.

If only one argument is provided, returns its value. If multiple arguments in a form of pair => value are provided, it sets the corresponding database parameters.

The authorised parameters are:


Can be overridden.










Can be overridden.


Can be overridden.


Can be overridden.


Can be overridden.


Can be overridden.


Can be overridden.


Can be overridden.


























Return the list of available drivers.

bind( [ @values ] )

If no values to bind to the underlying query is provided, bind simply activate the bind value feature.

If values are provided, they are allocated to the statement object and will be applied when the query will be executed.


  ## or
  $dbh->bind->where( "something" )
  ## or
  ## and then later
  $dbh->bind( 'thingy' )->select->fetchrow_hashref()

Activate caching.


Check that the driver set in $SQL_DRIVER in ~/etc/common.cfg is indeed available.

It does this by calling available_drivers.

copy( [ \%values | %values )

Provided with either a reference to an hash or an hash of key => value pairs, copy will first execute a select statement on the table object, then fetch the row of data, then replace the key-value pair in the result by the ones provided, and finally will perform an insert.

Return false if no data to copy were provided, otherwise it always returns true.

create_table( @parameters )

The idea is to create a table with the givern parameters.

This is currently heavily designed to work for PoPList. It needs to be rewritten.

data_sources( [ %options ] )

Given an optional list of options, this return the data source of the database handler.

data_type( [ \@types | @types ] )

Given a reference to an array or an array of data type, data_type will check their availability in the database driver.

If nothing found, it return an empty list in list context, or undef in scalar context.

If something was found, it returns a hash in list context or a reference to a hash in list context.


Return the name of the current database.


delete will format a delete query based on previously set parameters, such as where.

delete will refuse to execute a query without a where condition. To achieve this, one must prepare the delete query on his/her own by using the do method and passing the sql query directly.

  $tbl->where( "login" => "jack" );
  $tbl->limit( 1 );
  my $rows_affected = $tbl->delete();
  ## or passing the where condition directly to delete
  my $sth = $tbl->delete( "login" => "jack" );

Disconnect from database. Returns the return code.

  my $rc = $dbh->disconnect;
do( $sql_query, [ \%attributes, \@bind_values ] )

Execute a sql query directly passed with possible attributes and values to bind.

The attributes list will be used to prepare the query and the bind values will be used when executing the query.

It returns the statement handler or the number of rows affected.


  $rc = $dbh->do( $statement ) || die( $dbh->errstr );
  $rc = $dbh->do( $statement, \%attr ) || die( $dbh->errstr );
  $rv = $dbh->do( $statement, \%attr, @bind_values ) || die( $dbh->errstr );
  my $rows_deleted = $dbh->do(
       DELETE FROM table WHERE status = ?
  }, undef(), 'DONE' ) || die( $dbh->errstr );
enhance( [ @value ] )

Toggle the enhance mode on/off.

When on, the functions from_unixtime and unix_timestamp will be used on date/time field to translate from and to unix time seamlessly.


Get the currently set error.


Is just an alias for err.


Is just an alias for errstr.


Get the currently set error string.

fatal( [ 1 | 0 ] )

Toggles fatal mode on/off.

from_unixtime( [ @fields | \@fields ] )

Set the list of fields that are to be treated as unix time and converted accordingly after the sql query is executed.

It returns the list of fields in list context or a reference to an array in scalar context.

format_statement( [ \@data, \@order, $table ] )

Format the sql statement.

In list context, it returns 2 strings: one comma-separated list of fields and one comma-separated list of values. In scalar context, it only returns a comma-separated string of fields.

format_update( \@data | \%data | %data | @data )

Formats update query based on the following arguments provided:


An array of key-value pairs to be used in the update query. This array can be provided as the prime argument as a reference to an array, an array, or as the data element of a hash or a reference to a hash provided.

Why an array if eventually we build a list of key-value pair? Because the order of the fields may be important, and if the key-value pair list is provided, format_update honors the order in which the fields are provided.

format_update will then iterate through each field-value pair, and perform some work:

If the field being reviewed was provided to from_unixtime, then format_update will enclose it in the function FROM_UNIXTIME() as in:


If the the given value is a reference to a scalar, it will be used as-is, ie. it will not be enclosed in quotes or anything. This is useful if you want to control which function to use around that field.

If the given value is another field or looks like a function having parenthesis, or if the value is a question mark, the value will be used as-is.

If bind is off, the value will be escaped and the pair field='value' created.

If the field is a SET data type and the value is a number, the value will be used as-is without surrounding single quote.

If bind is enabled, a question mark will be used as the value and the original value will be saved as value to bind upon executing the query.

Finally, otherwise the value is escaped and surrounded by single quotes.

format_update returns a string representing the comma-separated list of fields that will be used.

getdefault( %default_values )

Does some preparation work such as :

  1. the date/time field to use the FROM_UNIXTIME and UNIX_TIMESTAMP functions

  2. removing from the query the fields to avoid, ie the ones set with the avoid method.

  3. set the fields alias based on the information provided with the alias method.

  4. if a field last_name and first_name exist, it will also create an alias name based on the concatenation of the 2.

  5. it will set the default values provided. This is used for UPDATE queries.

It returns a new DB::Object::Tables object with all the data prepared within.

group( @fields | \@fields )

Format the group by portion of the query.

It returns an empty list in list context of undef in scalar context if no group by clause was build. Otherwise, it returns the value of the group by clause as a string in list context and the full group by clause in scalar context.

In list context, it returns: $group_by

In scalar context, it returns: GROUP BY $group_by

insert( DB::Object::Statement SELECT object, \%key_value | %key_value )

Prepares an INSERT query using the field-value pairs provided.

If a DB::Object::Statement object is provided as first argument, it will considered as a SELECT query to be used in the INSERT query, as in: INSERT INTO my table SELECT FROM another_table

Otherwise, insert will build the query based on the fields provided.

In scalar context, it returns the result of execute and in list context, it returns the statement object.


Get the id of the primary key from the last insert.

limit( [ END, [ START, END ] ] )

Set or get the limit for the future statement.

If only one argument is provided, it is assumed to be the end limit. If 2 are provided, they wil be the start and end.

It returns a list of the start and end limit in list context, and the string of the LIMIT in scalar context, such as: LIMIT 1, 10

local( %params | \%params )

Not sure what it does. I forgot.

lock( $lock_id, [ $timeout ] )

Set a lock using a lock identifier and a timeout. By default the timeout is 2 seconds.

If the lock failed (NULL), it returns undef(), otherwise, it returns the return value.


When invoked, no_bind will change any preparation made so far for caching the query with bind parameters, and instead substitute the value in lieu of the question mark placeholder.


Disable caching of queries.


Prepares the ORDER BY clause and returns the value of the clause in list context or the ORDER BY clause in full in scalar context, ie. "ORDER BY $clause"

param( $param | %params )

If only a single parameter is provided, its value is return. If a list of parameters is provided they are set accordingly using the SET sql command.

Supported parameters are:


If unsupported parameters are provided, they are considered to be private and not passed to the database handler.

It then execute the query and return undef() in case of error.

Otherwise, it returns the object used to call the method.


Evals a SELECT 1 statement and returns 0 if errors occurred or the return value.

prepare( $query, \%options )

Prepares the query using the options provided. The options are the same as the one in DBI prepare method.

It returns a DB::Object::Statement object upon success or undef if an error occurred. The error can then be retrieved using errstr or error.

prepare_cached( $query, \%options )

Same as prepare except the query is cached.

query( $query, \%options )

It prepares and executes the given SQL query with the options provided and return undef() upon error or the statement handler upon success.

replace( DB::Object::Statement object, [ %data ] )

Just like for the INSERT query, replace takes one optional argument representing a DB::Object::Statement SELECT object or a list of field-value pairs.

If a SELECT statement is provided, it will be used to construct a query of the type of REPLACE INTO mytable SELECT FROM other_table

Otherwise the query will be REPLACE INTO mytable (fields) VALUES(values)

In scalar context, it execute the query and in list context it simply returns the statement handler.


This is used to reset a prepared query to its default values. If a field is a date/time type, its default value will be set to NOW()

It execute an update with the reseted value and return the number of affected rows.

reverse( [ true ])

Get or set the reverse mode.

select( [ \$field, \@fields, @fields ] )

Given an optional list of fields to fetch, select prepares a SELECT query.

If no field was provided, select will use default value where appropriate like the NOW() for date/time fields.

select calls upon tie, where, group, order, limit and local to build the query.

In scalar context, it execute the query and return it. In list context, it just returns the statement handler.

set( $var )

Issues a query to SET the given SQL variable.

If any error occurred, undef will be returned and an error set, otherwise it returns true.


It toggles sort mode on and consequently disable reverse mode.

stat( [ $type ] )

Issue a SHOW STATUS query and if a particular $type is provided, it will returns its value if it exists, otherwise it will return undef.

In absence of particular $type provided, it returns the hash list of values returns or a reference to the hash list in scalar context.


Queries the DBI state and return its value.

table( $table_name )

Given a table name, table will return a DB::Object::Tables object. The object is cached for re-use.

table_push( $table_name )

Add the given table name to the stack of cached table names.

tables( [ $database ] )

Connects to the database and finds out the list of all available tables.

Returns undef or empty list in scalar or list context respectively if no table found.

Otherwise, it returns the list of table in list context or a reference of it in scalar context.

tables_refresh( [ $database ] )

Rebuild the list of available database table.

Returns the list of table in list context or a reference of it in scalar context.

tie( [ %fields ] )

If provided a hash or a hash ref, it sets the list of fields and their corresponding perl variable to bind their values to.

In list context, it returns the list of those field-variable pair, or a reference to it in scalar context.

unix_timestamp( [ \@fields | @fields ] )

Provided a list of fields or a reference to it, this sets the fields to be treated for seamless conversion from and to unix time.

unlock( $lock_id )

Given a lock identifier, unlock releases the lock previously set with lock. It executes the underlying sql command and returns undef() if the result is NULL or the value returned otherwise.

update( %data | \%data )

Given a list of field-value pairs, update prepares a sql update query.

It calls upon where and limit as previously set.

It returns undef and sets an error if it failed to prepare the update statement. In scalar context, it execute the query. In list context, it simply return the statement handler.

use( $database )

Given a database, it switch to it, but before it checks that the database exists. If the database is different than the current one, it sets the multi_db parameter, which will have the fields in the queries be prefixed by their respective database name.

It returns the database handler.

use_cache( [ 0 | 1 ] )

Sets or get the use_cache parameter.

use_bind( [ 0 | 1 ] )

Sets or get the use_cache parameter.

variables( [ $type ] )

Query the SQL variable $type

It returns a blank string if nothing was found, or the value found.

where( %args )

Build the where clause based on the field-value hash provided.

It returns the where clause in list context or the full where clause in scalar context, ie "WHERE $clause"

_cache_this( $query )

Provided with a query, this will cache it for future re-use.

It does some check and maintenance job to ensure the cache does not get too big whenever it exceed the value of $CACHE_SIZE set in the main config file.

It returns the cached statement as an DB::Object::Statement object.

_clean_statement( \$query | $query )

Given a query string or a reference to it, it cleans the statement by removing leading and trailing space before and after line breaks.


Removes object attributes, namely where, selected_fields, group_by, order_by, limit, alias, avoid, local, and as_string

_make_sth( $package, $hashref )

Given a package name and a hashref, this build a statement object with all the necessary parameters.

It also sets the query time to the current time with the parameter query_time

It returns an object of the given $package.


Being called using a statement handler, this reset the object by removing all the parameters set by various subroutine calls, such as where, group, order, avoid, limit, etc.

_save_bind( $query_type )

This saves/cache the bin query and return the object used to call it.

_value2bind( $query, $ref )

Given a sql query and a array reference, _value2bind parse the query and interpolate values for placeholder (?).

It returns true.



Given a value, this returns a DB::Object::AND object. You can retrieve the value with value

This is used by where

    my $op = $dbh->AND( login => 'joe', status => 'active' );
    ## will produce:
    WHERE login = 'joe' AND status = 'active'


Given a value, this returns a DB::Object::NOT object. You can retrieve the value with value

This is used by where

    my $op = $dbh->AND( login => 'joe', status => $dbh->NOT( 'active' ) );
    ## will produce:
    WHERE login = 'joe' AND status != 'active'


Given a value, this returns a DB::Object::OR object. You can retrieve the value with value

This is used by where

    my $op = $dbh->OR( login => 'joe', login => 'john' );
    ## will produce:
    WHERE login = 'joe' OR login = 'john'


Copyright (c) 2019-2020 DEGUEST Pte. Ltd.


Jacques Deguest <>


DBI, Apache::DBI