File Coverage

lib/Test/DBIC/ExpectedQueries.pm

Criterion	Covered	Total	%
statement	143	162	88.2
branch	29	38	76.3
condition	9	14	64.2
subroutine	20	24	83.3
pod	3	8	37.5
total	204	246	82.9

=head1 NAME

Test::DBIC::ExpectedQueries - Test that only expected DBIx::Class queries are run

=head1 VERSION 2.000

Version 2.000 is out with a breaking change. If you're having issues
with your test suite, please see the L file for details.


=head1 DESCRIPTION

Ensure that only the DBIx::Class SQL queries you expect are executed
while a particular piece of code under test is run. Find the places in
your code where the unexpected queries are executed.


=head2 Avoiding the n+1 problem

When following a relation off a DBIC row object it's easy to overlook
the fact that it might be causing one query for each and every row in
the resultset. This can easily be solved by prefetching those
relations, but you have to know it happens first.

This module will help you finding unexpected queries, where they are
being caused, and to ensure you don't accidentally start running many
single-row queries in the future.



=head1 SYNOPSIS

=head2 Setup

    use Test::More;
    use Test::DBIC::ExpectedQueries;
    my $schema = ...; # Connect to a DBIx::Class schema

=head2 Simple

    my @book_rows = expected_queries(
        $schema,
        sub {
            $schema->resultset("Book")->find(34);
            $schema->resultset("Author")->create( ... );
            $schema->resultset("Book")->search( undef, { join => "author" } )->all;
        },
        {
            book   => {
                select      => "<= 2",
                stack_trace => 1,
            },
            author => { insert => undef  },
        },
    );


=head2 Flexible

    my $queries = Test::DBI::ExpectedQueries->new({ schema => $schema }});
    $queries->run(sub {
        $schema->resultset("Book")->find(34);
        $schema->resultset("Author")->create( ... );
    });
    my @book_rows = $queries->run(sub {
        $schema->resultset("Book")->search( undef, { join => "author" } )->all;
    });

    $queries->test({
        book   => { select => "<= 2"},
        author => { insert => undef },
    });



=head1 USAGE

You might already have a good idea of what queries are/should be
run. But often that's not the case.

Start by wrapping some DBIC application code in a test without any
specific limits. The default expectation for all tables is 0 queries
run. So the test will fail, and report all the executed queries it
didn't expect.

Now you know what's going on. Now you can add prefetches or caching
for queries that shouldn't happen and specify query limits for the
currently known behaviour.

Whether you want to nail down the expected queries with exact counts,
or just put wide-margin comparisons in place is up to you.


=head2 Finding the unexpected queries

Once you find unexpected queries made by your code, the next step is
eliminating them. But where are they called from?


=head3 Chained ResultSets

DBIC has this nice feature of chaining resultsets, which means you can
create a resultset and later modify it by adding things to the WHERE
clause, joining in other resultsets, add prefetching of relations or
whatever you need to do.

You can create small logical pieces of queries (and put them on their
corresponding Result/ResultSet classes) and then combine them in to
actual queries, expressed in higher level operation. This is very,
very powerful and one of the coolest features of DBIC.

There is a problem with passing around a resultset before finally
executing it though, and that is that it can often be tricky to find
exactly where it is being executed.

=head3 Following relations

The problem of finding the source of a database call isn't limited to
chained queries though. The same thing happens when you construct a
query, and then follow relations off of the main table. This is what
causes the n + 1 problem and you accidentally make n queries for
individual rows on top of the first one.

These additional queries might be a long way off from where the
initial query was made.


=head3 Show the stack trace

To solve this problem of where the queries originate you can tell
Test::DBIC::ExpectedQueries to show a C for particular
tables.

These call stacks may be quite deep, so you'll have to find the
unexpected queries first, and then enable the call stack for each of
them. That will also avoid spamming the test output with things you're
not interested in.


=head2 Return value from the test

For the subroutine C, and the method
C<$queries->run(...)>, the return value is whatever the subroutine
under test returned, so it's easy to wrap the DBIC code under test and
still get out the result.

It is context sensitive.


=head2 Executed queries vs resultsets

Only queries actually executed inside the test are being
monitored. This sounds obvious, but might be a source of problems.

Many DBIC methods are context sensitive, and in scalar context might
just return an unrealized resultset rather than execute a query and
return the resulting rows. If you're unsure, assigning the query to an
array will make it run in list context and therefore execute the SQL
query.


=head2 DBIC_TRACE

Normally, setting the ENV variable DBIC_TRACE can be used to "warn"
the DBIC queries.

Test::DBIC:ExpectedQueries uses the same mechanism as DBIC_TRACE, so
while the code is run under the test the normal DBIC_TRACE will not
happen.



=head1 SUBROUTINES

=head2 expected_queries( $schema, $sub_ref, $expected_table_operations = {} ) : $result | @result

Run $sub_ref and collect stats for queries executed on $schema, then
test that they match the $expected_table_operations.

Return the return value of $sub_ref->().

See the ANNOTATED EXAMPLES below for examples on how the
$expected_table_operations is used, but here's a simple example:

    {
        book   => { select => "<= 2", update => 3 },
        author => { insert => undef               },
        genre  => { select => 2, stack_trace => 1 },
    },


=over 4

=item *

Use table names as found in the raw SQL, not DBIC terms like resultset
and relation names. For relational queries, only the first main table
is collected.

=item *

Use SQL terms like "select", "insert", "update", "delete", not DBIC
terms like "create" and "search".

=item *

A number means exact match. Comparisons in a string means, well that.

=item *

Undef means any number of queries

=item *

If you need to see where the queries for a table are executed from,
use C 1>.

=back



=head1 METHODS

=head2 new({ schema => $schema }}) : $new_object

Create new test object.

$schema is a DBIx::Class::Schema object.


=head2 run( $sub_ref ) : $result | @result

Run $sub_ref->() and collect all DBIC queries being run.

Return the return value of $sub_ref->().

You can call $queries->run() multiple times to add to the collected
stats before finally calling $queries->test().


=head2 test( $expected_table_operations = {} ) : $is_passing

Test the collected queries against $expected_table_operations (see
above) and either pass or fail a Test::More test.

If the test fails, list all queries relating to the tables with
unexpected activity.

If anything failed to be identified as a known query, always list
those queries. But don't fail the test just because of it.

Reset the collected stats, so subsequent calls to ->run() start with a
clean slate.



=head1 ANNOTATED EXAMPLES

=head2 Simple interface

    use Test::More;
    use Test::DBIC::ExpectedQueries;

    my $schema = ...;  # A DBIx::Class schema object

    # The return value of the subref is returned
    my $author_rows = expected_queries(
        # Collect stats for this schema
        $schema,
        # when running this code
        sub {
            $author_tree->create_authors_for_tabs($schema),
        },
        # and ensure these are the expected queries
        {
            # For the "tree_node" table
            tree_node => {
                update => ">= 1",  # Number of updates must be >= 1
                select => undef,   # Any number of selects are fine
            },
            # For the "author" table
            author => {
                update      => 8,  # Number of updates must be exactly 8
                stack_trace => 1,  # Show stack trace if it fails
            },
            user_session => {
                delete => "< 10",  # No more than 9 deletes allowed
            },
            # Any query on any other table will fail the test
        },
    );


=head2 Flexible interface

Using the OO interface allows you to collect stats for many separate
queries.

It is also useful for when you care about individual return values
from methods called, and when you don't know the expected number of
queries until after they have been run.

    use Test::More;
    use Test::DBIC::ExpectedQueries;

    my $queries = Test::DBIC::ExpectedQueries->new({ schema => $schema });
    my $author_rows = $queries->run(
        sub { $author_tree->create_authors_for_tabs($schema) },
    );

    # Add more stats in a second run
    $queries->run( sub { $author_tree->check_stuff() } );

    # ... test other things

    my $total_author_count = @{$author_rows} + 1; # or whatever

    # This resets the collected stats
    $queries->test(
        {
            author     => {
                insert => $total_author_count,
                update => undef,
            },
            field      => { select => "<= 1" },
            tree_node  => { select => 2 },
        },
    );

=cut

package Test::DBIC::ExpectedQueries;
$Test::DBIC::ExpectedQueries::VERSION = '2.000';
use Moo;
use Exporter::Tiny;
BEGIN {extends "Exporter::Tiny"};
our @EXPORT = "expected_queries";


use Test::More;
use Try::Tiny;
use Carp;
use DBIx::Class;
use Devel::StackTrace;

use Test::DBIC::ExpectedQueries::Query;



### Simple procedural interface

sub expected_queries {
    my ($schema, $subref, $expected) = @_;
    $expected ||= {};
    local $Test::Builder::Level = $Test::Builder::Level + 1;

    my $queries = Test::DBIC::ExpectedQueries->new({ schema => $schema });

    my $return_values;
    if (wantarray()) {
        $return_values = [ $queries->run($subref) ];
    }
    else {
        $return_values = [ scalar $queries->run($subref) ];
    }

    $queries->test($expected);

    return @$return_values if wantarray();
    return $return_values->[0];
}



### Full OO interface

has schema => (
    is       => "ro",
    required => 1,
);

has queries => (
    is      => "rw",
    default => sub { [] },
    trigger => sub { shift->clear_table_operation_count },
    lazy    => 1,
    clearer => 1,
);

has table_operation_count => (
    is      => "lazy",
    clearer => 1,
);
sub _build_table_operation_count {
    my $self = shift;

    my $table_operation_count = {};
    for my $query (grep { $_->operation } @{$self->queries}) {
        $table_operation_count->{ $query->table }->{ $query->operation }++;
    }

    return $table_operation_count;
}

has ignore_classes => ( is => "lazy" );
sub _build_ignore_classes {
    my $self = shift;
    return [
        # "main",
        "Test::DBIC::ExpectedQueries",
        "Class::MOP::Method::Wrapped",
        "Moose::Meta::Method::Delegation",
        "Context::Preserve",
        # "DBIx::Class",
        # "DBIx::Class::Schema",
        # "DBIx::Class::Storage::BlockRunner",
        "DBIx::Class::ResultSet",
        "DBIx::Class::Row",
        "DBIx::Class::Storage::DBI",
        "DBIx::Class::Storage::Statistics",
        "DBIx::Class::Row",
        "Test::Builder",
        "Test::Class",
        "Test::Class::Moose",
        "Test::Class::Moose::Runner",
        "Test::Class::Moose::Report::Method",
        "Test::Class::Moose::Role::Executor",
        "Test::Class::Moose::Executor::Sequential",
        "Try::Tiny",
        "Try::Tiny::Catch",
    ];
}

sub _stack_trace {
    my $self = shift;

    my $trace = Devel::StackTrace->new(
        message      => "executed",
        ignore_class => $self->ignore_classes,
    );

    my $callers = $trace->as_string;
    chomp($callers);
    $callers =~ s/\n/ <-- /gsm;
    $callers =~ s/=?(HASH|ARRAY)\(0x\w+\)/<$1>/gsm;

    return $callers;
}

sub run {
    my $self = shift;
    my ($subref) = @_;
    my $wantarray = wantarray(); # Avoid it being masked in side try-catch block

    my $storage = $self->schema->storage;

    my $previous_debug = $storage->debug();
    $storage->debug(1);

    my @queries;
    my $previous_callback = $storage->debugcb();
    $storage->debugcb( sub {
        my ($op, $sql) = @_;
        ###JPL: don't ignore the $op, use it instead of parsing out
        ###the operation?
        chomp($sql);
        push(
            @queries,
            Test::DBIC::ExpectedQueries::Query->new({
                sql         => $sql,
                stack_trace => $self->_stack_trace(),
            }),
        );
    } );

    my $return_values;
    try {
        if ($wantarray) {
            $return_values = [ $subref->() ];
        }
        else {
            $return_values = [ scalar $subref->() ];
        }
    }
    catch { die($_) }
    finally {
        $storage->debugcb($previous_callback);
        $storage->debug($previous_debug);
    };

    $self->queries([ @{$self->queries}, @queries ]);

    return @$return_values if $wantarray;
    return $return_values->[0];
}

sub test {
    my $self = shift;
    my ($expected) = @_;
    $expected ||= {};
    local $Test::Builder::Level = $Test::Builder::Level + 1;

    my $failure_message = $self->check_table_operation_counts($expected);
    my $unknown_warning = $self->unknown_warning;

    $self->clear_queries();
    $self->clear_table_operation_count();


    my $test_description = "Expected queries for tables";
    if($failure_message) {
        fail("$test_description:\n\n$failure_message$unknown_warning");
        return 0;
    }

    pass("$test_description$unknown_warning");
    return 1;
}

sub check_table_operation_counts {
    my $self = shift;
    my ($expected_table_count) = @_;

    my $table_operation_count = $self->table_operation_count();

    # Check actual events against test spec
    my $expected_all_operation = $expected_table_count->{_all_} || {};
    my $table_test_result = {};
    for my $table (sort keys %{$table_operation_count}) {
        my $operation_count = $table_operation_count->{$table};

        for my $operation (sort keys %$operation_count) {
            my $actual_count = $operation_count->{$operation};
            my $expected_outcome = do {
                if ( exists $expected_table_count->{$table}->{$operation} ) {
                    $expected_table_count->{$table}->{$operation};
                }
                elsif (exists $expected_all_operation->{$operation}) {
                    $expected_all_operation->{$operation};
                }
                else { 0 }
            };
            defined($expected_outcome) or next;

            my $test_result = $self->test_count(
                $table,
                $operation,
                $expected_outcome,
                $actual_count,
            );
            $test_result and push(@{ $table_test_result->{$table} }, $test_result);
        }
    }

    # Check test spec against actual events to catch
    ###JPL: extend this to validate test operations
    my $operation_to_test = {
        select => 1,
        insert => 1,
        update => 1,
        delete => 1,
    };
    for my $table (sort keys %$expected_table_count) {
        my $expected_operation_count = $expected_table_count->{$table};
        for my $operation (sort keys %$expected_operation_count) {
            next if ! $operation_to_test->{$operation};
            # Already tested?
            next if exists $table_operation_count->{$table}->{$operation};

            my $expected_outcome = $expected_operation_count->{$operation};
            defined $expected_outcome or next; # undef = ignore

            my $actual_count = $table_operation_count->{$table}->{$operation} || 0;
            my $test_result = $self->test_count(
                $table,
                $operation,
                $expected_outcome,
                $actual_count,
            );
            $test_result and push(@{ $table_test_result->{$table} }, $test_result);
        }
    }

    if(scalar keys %$table_test_result) {
        my $message = "";
        for my $table (sort keys %{$table_test_result}) {
            $message .= "* Table: $table\n";
            $message .= join("\n", @{$table_test_result->{$table}});
            $message .= "\nActually executed SQL queries on table '$table':\n";
            $message .= $self->sql_queries_for_table(
                $table,
                $expected_table_count,
            ) . "\n\n";
        }
        return $message;
    }
    return "";
}

sub unknown_warning {
    my $self = shift;

    my @unknown_queries = $self->unknown_queries() or return "";

    return "\n\nWarning: unknown queries:\n" . join(
        "\n",
        map { $_->display_sql } @unknown_queries,
    ) . "\n";
}

sub unknown_queries {
    my $self = shift;
    return grep {  ! $_->operation } @{$self->queries};
}

sub sql_queries_for_table {
    my $self = shift;
    my ($table, $expected_table_count) = @_;

    my $stack_trace = $expected_table_count->{$table}->{stack_trace} || 0;

    return join(
        "\n",
        map  {
            my $out = $_->display_sql;
            $stack_trace and $out .= "\n" . $_->display_stack_trace;
            $out;
        }
        grep { lc($_->table // "") eq lc($table // "") }
        @{$self->queries},
    );
}

sub test_count {
    my $self = shift;
    my ($table, $operation, $expected_outcome, $actual_count) = @_;

    my $expected_count;
    my $operator;
    if($expected_outcome =~ /^ \s* (\d+) /x) {
        $operator = "==";
        $expected_count = $1;
    }
    elsif($expected_outcome =~ /^ \s* (==|!=|>|>=|<|<=) \s* (\d+) /x) {
        $operator = $1;
        $expected_count = $2;
    }
    else {
        croak("expect_queries: invalid comparison ($expected_outcome)\n");
    }

    #                            actual,                expected
    my $comparison_perl = 'sub { $_[0] ' . $operator . ' $_[1] }';
    my $comparison = eval $comparison_perl; ## no critic
    $comparison->($actual_count, $expected_count) and return "";

    return "Expected '$expected_outcome' ${operation}s for table '$table', got '$actual_count'";
}

1;



__END__