NAME¶
UR::DataSource::Filesystem - Get and save objects to delimited text files
SYNOPSIS¶
# Create an object for the data file
my $people_data = UR::DataSource::Filesystem->create(
columns => ['person_id','name','age','street_address'],
sorted_columns => ['age','person_id'],
path => '/var/lib/people/$state/$city/people.txt',
delimiter => "\t", # between columns in the file
record_separator => "\n", # between lines in the file
);
# Define an entity class for the people in the file
class MyProgram::Person {
id_by => 'person_id',
has => [
name => { is => 'String' },
age => { is => 'Number' },
street_address => { is => 'String' },
city => { is => 'String' },
state => { is => 'String' },
],
data_source_id => $people_data->id,
};
# Get all people that live in any city named Springfield older than 40
my @springfielders = MyProgram::Person->get(city => 'Springfield', 'age >' => 40);
DESCRIPTION¶
A Filesystem data source object represents one or more files on the fileystem.
In the simplest case, the object's 'path' property names a file that stores
the data.
Properties¶
These properties determine the configuration for the data source.
- path <string>
- path is a string representing the path to the files. Besides just being a
simple pathname to one file, the string can also be a specification of
many similar files, or a directory containing multiple files. See below
for more information about 'path'
- record_separator <string>
- The separator between lines in the file. This gets stored in $/ before
calling getline() to read data. The default record_separator is
"\n".
- delimiter <string>
- The separator between columns in the file. It is used to construct a regex
with qr() to split() a line into a list of values. The
default delimiter is '\s*,\s*', meaning that the file is separated by
commas. Another common value would be "\t" for tabs.
- columns <ARRAY>
- A listref of column names in the file. Just as SQL tables have columns,
Filesystem files also have named columns so the system knows how to read
the file data into object properties. A Filesystem data source does not
need to specify named columns if the 'columns_from_header' property is
true.
Classes that use the Filesystem data source attach their properties to the
data source's columns via the 'column_name' metadata. Besides the columns
directly named in the 'columns' list, two additional column-like tokens
may be used as a column_name: '__FILE__' and '$.'. __FILE__ means the
object's property will hold the name of the file the data was read from.
$. means the value will be the input line number from the file. These are
useful when iterating over the contents of a file. Since these two fake
columns are always considered "sorted", it makes reading from
the file faster in some cases. See the 'sorted_columns' discussion below
for more information.
- sorted_columns <ARRAY>
- A listref of column names that the file is sorted by, in the order of the
sorting. If a column is sorted in descending order, put a minus (-) in
front of the name. If the file is sorted by multiple columns, say first by
last_name and then by first_name, then include them both:
sorted_columns => ['last_name','first_name']
The system uses this information to know when to stop reading if a query is
done on a sorted column. It's also used to determine whether a query done
on the data source matches the sort order of the file. If not, then the
data must be gathered in two passes. The first pass finds records in the
file that match the filter. After that, the matching records are sorted in
the same way the query is requesting before returning the data to the
Context.
The Context expects incoming data to always be sorted by at least the class'
ID properties. If the file is unsorted and the caller wants to be able to
iterate over the data, then it is common to have the class' ID properties
specified like this:
id_by => [
file => { is => 'String', column_name => '__FILE__' },
line => { is => 'Integer', column_name => '$.' },
]
Otherwise, it will need to read in the whole file and sort the contents
before returning the first row of data from its iterator.
- columns_from_header <boolean>
- If true, the system will read the first line of the file to determine what
the column names are.
- header_lines <integer>
- The number of lines at the top of the file that do not contain entity
data. When the file is opened, this number of lines are skipped before
reading data. If the columns_from_header flag is true, the header_lines
value should be at least 1.
- handle_class <string>
- Which class to use for reading and writing to the file. The default is
IO::File. Any other value must refer to a class that has the same
interface as IO::File, in particular: new, input_line_number, getline,
tell, seek and print.
Path specification¶
Besides refering to just one file on the filesystem, the path spec is a recipe
for finding files in a directory tree. If a class using a Filesystem data
source does not have 'table_name' metadata, then the path specification must
resolve to file names. Alternatively, classes may specify their 'table_name'
which is interpreted as a file within the directory indicated by the path
specification.
Three kinds of special tokens can also appear in a file spec:
- $property
- When querying, the system will extract the value (or values, for an
in-clause) of $property from the BoolExpr when constructing the pathname.
If the BoolExpr does not have a value for that property, then the system
will do a shell glob to find the possible values. For example, given this
path spec and query:
path => '/var/people/$state/$city/people.txt'
my @people = MyProgram::People->get(city => 'Springfield', 'age >' => 40);
it would find the data files using the glob expression
/var/people/*/Springfield/people.txt
It also knows that any objects coming from the file
/var/people/CA/Springfield/people.txt
must have the value 'CA' for their 'state' property, even though that
information is not in the contents of the file.
When committing changes back to the file, the object property values are
used to determine which file it should be saved to.
The property name can also be wrapped in braces:
/var/people/${state}_US/city_${city}/people.txt
- &method
- The replacement value is resolved by calling the named method on the
subject class of the query. The method is called like this:
$replacement = $subject_class->$method( $boolexpr_or_object);
During a query, the method is passed a BoolExpr; during a commit, the method
is passed an object. It must return a string.
The method name can also be wrapped in braces:
/&{resolve_prefix}.dir/people.txt
- *, ?
- Literal shell glob wildcards are honored when finding files, but their
values are not used to supply values to objects.
Environment Variables¶
If the environment variable $UR_DBI_MONITOR_SQL is true, then the Filesystem
data source will print information about the queries it runs.
INHERITANCE¶
UR::DataSource
SEE ALSO¶
UR, UR::DataSource