=head1 NAME DBIx::DataModel::Doc::Quickstart - Get quickly started with DBIx::DataModel =head1 DOCUMENTATION CONTEXT This chapter is part of the C manual. =over =item * L =item * L =item * QUICKSTART =item * L =item * L =item * L =item * L =back This chapter is a tutorial that shows the main steps to get started with C. The goal here is conciseness, not completeness; a full reference is given in the L chapter. The tutorial is a gentle expansion of the examples given in the L, namely a small human resources management system. =head1 BASIC ASSUMPTIONS Before starting with C, you should have installed CPAN modules L and L. You also need a database management system with a L driver. Use your database modeling tool to create some tables for employees, departments, activities (an employee working in a department from a start date to an end date), and employee skills. If you have no modeling tool, you can also feed something like the following SQL code to the database CREATE TABLE t_employee ( emp_id INTEGER AUTO_INCREMENT PRIMARY KEY, lastname TEXT NOT NULL, firstname TEXT, d_birth DATE ); CREATE TABLE t_department ( dpt_code VARCHAR(5) PRIMARY KEY, dpt_name TEXT NOT NULL ); CREATE TABLE t_activity ( act_id INTEGER AUTO_INCREMENT PRIMARY KEY, emp_id INTEGER NOT NULL REFERENCES t_employee(emp_id), dpt_code VARCHAR(5) NOT NULL REFERENCES t_department(dpt_code), d_begin DATE NOT NULL, d_end DATE ); CREATE TABLE t_skill ( skill_code VARCHAR(2) PRIMARY KEY, skill_name TEXT NOT NULL ); CREATE TABLE t_employee_skill ( emp_id INTEGER NOT NULL REFERENCES t_employee(emp_id), skill_code VARCHAR(2) NOT NULL REFERENCES t_skill(skill_code), CONSTRAINT PRIMARY KEY (emp_id, skill_code) ); As can be seen from this SQL, we assume that the primary keys for C and C are generated automatically by the RDBMS. Primary keys for other tables are character codes and therefore should be supplied by the client program. We decided to use the suffixes C<_id> for auto-generated keys, and C<_code> for user-supplied codes. =head1 DECLARE SCHEMA AND TABLES C needs to acquire some knowledge about the datamodel. The rest of this chapter will go through the steps to manually write the necessary declarations, which are quite concise; however, you may gain some time by using L to automatically create a skeleton of these declarations. First declare a I : use DBIx::DataModel; DBIx::DataModel->Schema('HR'); Here we have chosen a simple acronym C
as the schema name, but it could as well have been something like C. The schema now is a Perl class, so we invoke its C method to declare the first table within the schema : HR->Table(qw/Employee t_employee emp_id/); This creates a new Perl class named C (the schema name C
has been automatically prepended before the table name). The second argument C is the database table, and the third argument C is the primary key. So far nothing is declared about other columns in the table. Other tables are declared in a similar fashion : HR->Table(qw/Department t_department dpt_code/); HR->Table(qw/Activity t_activity act_id/); HR->Table(qw/Skill t_skill skill_code/); HR->Table(qw/EmployeeSkill t_employee_skill emp_id skill_code/); This last declaration has 4 arguments because the primary key ranges over 2 columns. =head1 DECLARE COLUMN TYPES RDBMS will usually require that dates be in ISO format of shape C. Let's assume our users are European and want to see and enter dates of shape C. Insert of converting back and forth within the client code, it's easier to do it at the ORM level. So we define conversion routines within a "Date" column type HR->ColumnType(Date => fromDB => sub {$_[0] =~ s/(\d\d\d\d)-(\d\d)-(\d\d)/$3.$2.$1/ if $_[0]}, toDB => sub {$_[0] =~ s/(\d\d)\.(\d\d)\.(\d\d\d\d)/$3-$2-$1/ if $_[0]}, validate => sub {$_[0] =~ m/\d\d\.\d\d\.\d\d\d\d/}); and then apply this type to the appropriate columns HR::Employee->ColumnType(Date => qw/d_birth/); HR::Activity->ColumnType(Date => qw/d_begin d_end/); Here we just perform scalar conversions; another design choice could be to "inflate" the data to some kind of Perl objects. Observe that C is overloaded : when invoked on a schema, it I a column type; when invoked on a table, it I the column type to some columns. =head1 DECLARE ASSOCIATIONS =head2 Basic associations Now we will declare a binary association between departements and activities: HR->Association([qw/Department department 1 /], [qw/Activity activities * /]); The C method takes two references to lists of arguments; in each of them, we find : class name, role name, multiplicity, and optionally the names of columns participating in the join. Here column names are not specified, so the method assumes that the join is on C (from the primary key of the class with multiplicity 1 in the association). This declaration corresponds to the following UML diagram : +----------------+ +--------------+ | | 1 * | | | HR::Department +----------------------------+ HR::Activity | | | department activities | | +----------------+ +--------------+ Like when reading the diagram, the declaration should be read crosswise : here we are stating that a department may be associated with several activities; therefore the C class will contain an C method which returns an arrayref. Conversely, an activity is associated with exactly one department, so the C class will contain a C method which returns a single instance of C. Since associations are symmetric, the two arrayrefs in the C declaration could as well be given in the reverse order, yielding exactly the same effect. =head3 Choosing role names Technically, a role name can be any valid Perl identifier, so it can be chosen arbitrarily; however, in most cases it is a good idea to take the name of the associated table : this will make it easier to follow method calls and joins that navigate between tables. In addition, it is also a good idea to use role names in I when the multiplicity is 1, and in I when the multiplicity is greater than 1, again for readability reasons. One exception to this recommendation is when there are several associations between the same tables, in which case role names are precisely useful to make the distinction. For example, suppose that each department has offices in one or several buildings, and has its address in one building: this could be modeled with one pair of roles C / C, and one other pair of roles C / C. =head2 Compositions The second association could be defined in a similar way; but here we will introduce the new concept of I. HR->Composition([qw/Employee employee 1 /], [qw/Activity activities * /]); This looks exactly like an association declaration; but it states that an activity somehow "belongs" to an employee (cannot exist without being attached to an employee, and is often created and deleted together with the employee). In a UML class diagram, this would be pictured with a black diamond on the Employee side. Using a composition instead of an association in this particular example would perhaps be debated by some data modelers; but at least it allows us to illustrate the concept. A composition declaration behaves in all respects like an association. The main difference is in C and C methods, which will be able to perform more complex operations on data trees : for example it will be possible in one method call to insert an employee together with its activities. Compositions also support auto-expansion of data trees through the L method. =head2 Many-to-many associations Now comes the association between employees and skills, which is a many-to-many association. This happens in two steps: first we declare as usual the associations with the linking table : HR->Association([qw/Employee employee 1 /], [qw/EmployeeSkill emp_skills * /]); HR->Association([qw/Skill skill 1 /], [qw/EmployeeSkill emp_skills * /]); Then we declare the many-to-many association: HR->Association([qw/Employee employees * emp_skills employee/], [qw/Skill skills * emp_skills skill /]); This looks almost exactly like the previous declarations, except that the last arguments are no longer column names, but rather I: these are the sequences of roles to follow in order to implement the association. This example is just an appetizer; more explanations are provided in the reference section. =head1 USE THE SCHEMA To use the schema, we first need to supply it with a database connection : my $dbh = DBI->connect(...); # parameters according to your RDBMS HR->dbh($dbh); # give $dbh handle to the schema Now we can start populating the database: my ($bach_id, $berlioz_id, $monteverdi_id) = HR::Employee->insert([qw/ firstname lastname /], [qw/ Johann Bach /], [qw/ Hector Berlioz /], [qw/ Claudio Monteverdi /]); This form of C, supplying a list of arrayrefs with column names in the first arrayref, is convenient for inserting a bunch of rows at once. The other form is to supply one or several hashrefs, where each hashref corresponds to a record to create, and yields the same result : HR::Employee->insert({firstname => "Johann", lastname => "Bach" }, {firstname => "Hector", lastname => "Berlioz" }, {firstname => "Claudio", lastname => "Monteverdi"}); According to our earlier assumptions, keys are generated automatically within the database, so they need not be supplied here. The return value of the method is the list of generated ids (provided that your database driver supports DBI's L method). Similarly, we create some departments and skills (here with explicit primary keys, and using both insertion syntaxes) : HR::Department->insert({dpt_code => "CPT", dpt_name => "Counterpoint" }, {dpt_code => "ORCH", dpt_name => "Orchestration"}); HR::Skill->insert([qw/ skill_code skill_name /], [qw/ VL Violin /], [qw/ KB Keyboard /], [qw/ GT Guitar /]); To perform updates, there is either a class method or an object method. Here is an example with the class method : HR::Employee->update($bach_id => {firstname => "Johann Sebastian"}); Associations have their own insert methods, named C : my $bach = HR::Employee->fetch($bach_id); # get single record from prim.key $bach->insert_into_activities({d_begin => '01.01.1695', d_end => '18.07.1750', dpt_code => 'CPT'}); $bach->insert_into_emp_skills({skill_code => 'VL'}, {skill_code => 'KB'}); Compositions implement cascaded inserts from a given data tree : HR::Employee->insert({firstname => "Richard", lastname => "Strauss", activities => [ {d_begin => '01.01.1874', d_end => '08.09.1949', dpt_code => 'ORCH' } ]}); The C method retrieves several records from a class : my $all_employees = HR::Employee->select; foreach my $emp (@$all_employees) { do_something_with($emp); } or maybe we want something more specific : my @columns = qw/firstname lastname/; my %criteria = (lastname => {-like => 'B%'}); my $some_employees = HR::Employee->select(-columns => \@columns, -where => \%criteria, -orderBy => 'd_birth'); From a given object, role methods allow us to get associated objects : foreach my $emp (@$all_employees) { print "$emp->{firstname} $emp->{lastname} "; my @skill_names = map {$_->{skill_name} }} @{$emp->skills}; print " has skills ", join(", ", @skill_names) if @skill_names; } Passing arguments to role methods, we can restrict to specific columns or specific rows, exactly like the C method : my @columns = qw/d_begin d_end/; my %criteria = (d_end => undef); my $current_activities = $someEmp->activities(-columns => \@columns, -where => \%criteria); And it is possible to join on several roles at once: my $result = $someEmp->join(qw/activities department/) ->select(-columns => \@columns, -where => \%criteria); This concludes our short tutorial. More examples are given in the L chapter.