Risc World 3/Risc World 3.iso/SOFTWARE/ISSUE4/POWERBASE/DOCS/Ch08-CSVs

Text File | 2001-01-29 | 18KB | 326 lines

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Ch 8 − Using CSV files
======================

8.1     What are CSV files?
---------------------------
CSV stands for “comma-separated values” and is the name given to files
consisting of lines of data, each of which contains individual data items
separated from each other by commas. Such files are widely used to
mail-merge using a wordprocessor (see Ch 9) and also to transfer data from
one application to another, e.g. from a database to a spreadsheet or from a
RISC OS database to a PC database. We will refer to each line in a CSV file
as a record and each item of data in such a line as a field since records
and fields are the source and destination of such data when it is exported
from or imported into a Powerbase database. The following points should be
noted:

(1) Fields which are non-numeric (e.g. plain text items such as names and
addresses) are often enclosed in double quotes (“”) whereas numeric data is
not. This makes it possible for an application reading a CSV file to
distinguish between numbers and strings (which might of course contain
numerals) and also allows a comma to be used as a character within a string
without being mistaken for a data separator. (Addresses often contain commas
e.g. 112, Keighley Road).  For many purposes the quotes aren’t necessary and
may be omitted.

(2) Null fields are usually included and can be located by looking for two
commas with either nothing in between them or with only two double quotation
marks between them, i.e. ,, or ,“”,. Each record in such a file will always
contain the same number of fields. Powerbase does, however, allow nulls to
be omitted entirely when creating a file in which case the number of fields
per record will vary.

(3) The way in which each record is terminated varies from one system to
another. The last field in a record is followed not by a comma but by a line
terminator. On RISC OS systems this is the same as in ordinary text files:
the linefeed character (LF, ASCII value 10) and on PCs it is usually the
carriage-return character (CR, ASCII value 13). You might, however,
encounter CSV files in which both these characters are used, i.e. LF CR or
CR LF. Powerbase lets you define any character or pair of characters as the
record terminator.

(4) Separators other than commas are sometimes used. The Tab character
(ASCII value 9) is often used and such files are called TSV (“tab-separated
values”) files. Powerbase lets you define any character, or even a pair of
characters, as the field separator. All such files created by Powerbase will
be of type &dfe and display the CSV file icon (although the default
filenames offered do differ: “CSVfile” where the separator really is a
comma, “TSVfile” where it’s a TAB and “?SVfile” otherwise). In what follows
we will, for convenience, refer to them all as “CSV files” whether or not
the separator is a comma.

(5) Some applications which accept a CSV file as input expect the first line
to contain the names of the fields which comprise the subsequent records,
e.g. if each record consists of a name and a four-part address this header
record might read:

        “NAME”,“STREET”,“TOWN”,“COUNTY”,“POSTCODE”

Powerbase can both export and import files with such a header.

8.2     Setting the CSV options
-------------------------------
Choosing CSV files => Options from the main menu displays the CSV options
window which lets you specify all the file characteristics described
earlier.  Pop-up menus give you a choice of field-separators and
record-terminators with space to enter your own if you wish.  The first
three option switches cause an exported file to have, respectively, the
following characteristics when the switch is selected:

•       quotes round non-numeric fields − see (1) above

•       a header record specifying the field names as either tags or
        descriptors − see (5) above

•       null fields included − see (2) above

Note that the field names referred to in a header record are, by default,
the tags of the corresponding Powerbase fields, but may be changed to the
descriptors by altering the setting in the Print options window.

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8.3     Exporting data as a CSV file
------------------------------------
Having set up your options as described above, creating a CSV file is very
like printing a list. First highlight the fields to be exported by clicking
on each with ADJUST. Remember that the order in which the fields are
highlighted is important. Next choose CSV files =>Export (Ctrl X). A window
featuring the Query panel appears. Type in a search formula to determine
which records are exported. Finally, enter the name of the file and drag the
file icon to a filer window. By default the file is saved in PrintJobs as
usual, and you may simply click on the Export button or type Return.
Experiment with saving CSV files with different settings of the CSV options
and then loading the resulting files into Edit to examine them.  If you
select the Reverse switch on the Query panel the CSV file will be created in
reverse order. (See also 3.5.1).

The field-concatenation option (see 3.2.2) applies.  This means that data
which occupies separate fields in the Powerbase record need not do so in the
exported CSV file.  By holding down Shift when selecting the field with
ADJUST, the comma (or other separator) which would normally follow is
suppressed until you select a field without using Shift.  A slightly
problematic situation occurs when you concatenate a mixture of numeric and
non-numeric fields with the In quotes option selected.  In such a case
Powerbase will enclose the whole concatenated group within two sets of
double quotes. e.g. NAME, Z, M and SYM from the Elements database would be
exported, for actinium, as:

        “ACTINIUM 89 227 Ac”

The Spacer (see 3.10) − in the above instance it is the default setting of
one space − is used to separate the concatenated fields.

8.3.1   Scrollable lists and CSV files

Scrollable fields may appear in a CSV file in two different ways, depending
on how their printing option is set in the Print Options window. If As
single row is selected the whole list is exported as a single CSV field. The
data corresponding to individual rows of the list are separated by
semicolons. If As columns is selected then each row of the list is exported
as a CSV field.

Transferring data from and to scrollable lists in individual records was
covered in 2.6.5 and 2.6.6.

8.4     Using CSV files to import data
--------------------------------------
If you drop a CSV file on the record window of an open database the CSV
options window (see 8.2) appears with the title changed to “Import CSV file”
and some additional icons, one of which displays the pathname of the file.
Clicking on Import will make Powerbase try to create new database records
from the file. If you decide not to do this you should click on Cancel. If
you do wish to import the data there are some important consideration which
will now be explained.

8.4.1   Ensuring that the correct options are selected

If the CSV file originally came from a Powerbase application the settings in
the CSV options window need to be exactly the same as they were when the
file was exported. The exception to this is the In quotes button which is
shaded on import because Powerbase doesn’t need it. If the CSV file came
from a PC or another RISC OS application you might have to load it into Edit
to find out what separator and terminator are used.  You will also probably
need to set the filetype to &dfe (omit the “&”) as well.

There are three more option switches at the bottom of the window. One causes
each record to be displayed as it is imported. The import process is slower
with this turned on but much more informative if you like to know how things
are progressing. The second switch, when selected, strips any trailing
spaces in the imported data-fields. Some database programs pad all fields to
their maximum length by adding spaces to the end of the data where
necessary.  If you import such a file into Powerbase you will find that the
caret will always be at the far right of the field even though visible
characters do not fill the field, and some queries won’t work properly.
Setting the Strip spaces switch before importing the file overcomes the
problem.  The third option switch determines how Sequence number fields are
handled.  If the switch is ON imported sequence numbers are ignored and new
ones assigned in accordance with the field’s sequence number counter.  With
the switch OFF sequence numbers from the CSV file are imported without
alteration.

8.4.2   Directing imported data to the correct fields

If no fields on the record window are highlighted (i.e. with ADJUST) and the
CSV file does not contain a header record (see 8.1) then the import process
proceeds according to the following rules:

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•       The first CSV field will be read into the first Powerbase field for
        which importing is allowed, This means any which can hold text
        (including External fields) or numbers and also check-boxes Graphics
        fields, Buttons or fields which are merely labels will be ignored.
        The next CSV field will be read into the second Powerbase field and
        so on.

•       If the end of the CSV record is reached before all the relevant
        fields have been filled (data underflow) then the next CSV record
        will start a new Powerbase record, i.e. the reading won’t get out of
        step. It does not matter, therefore, if the CSV file omits null
        items at the end of a line.

•       If all relevant fields are filled before reaching the end of the CSV
        record (data overflow) Powerbase ignores the remainder of the line
        and skips to the beginning of the next CSV record before starting a
        new Powerbase record. This is also to keep the operation in step.

There will be occasions when you don’t want to fill the Powerbase fields
sequentially as just described. There are two ways of making the process
more specific:

(1) Highlight the required Powerbase fields with ADJUST before starting the
import.  Data will then be read only into the highlighted fields, all other
fields being ignored. The order in which the fields are filled is the order
in which you highlighted them.  The rules given above about underflow and
overflow of data still apply.

(2) Give the file a header record containing the tags or descriptors of
required fields in the Powerbase record.  There is nothing to prevent you
using Edit  to add such a header to a CSV file which did not originate from
a Powerbase application. The format of the header is illustrated in 8.1 (5).
Importing then occurs just as if those fields were highlighted. The Print
options window must reflect whether the tags or descriptors of fields are
used. Do not use both a header and highlighting.

8.4.3   Importing data from plain text files

It was explained in 8.1 (4) that files created as described above (8.3) can
have separators other than a comma. If the file has been created using
Powerbase’s CSV exporting facility it will have been given the file-type
&dfe as if it was a true CSV file. If it comes from some other source it is
likely to be of type &fff (Text). It can still be imported but caution is
needed because there are other circumstances in which a text file might be
dropped on the record window. A properly-written script file (see Ch 12)
would be recognised as such and therefore cause no problem, but any text
file dropped onto the appropriate type of External field (i.e. a Text or
Text Block field) would become linked to that field instead of being treated
like a CSV file. If you are importing data from a plain text file and your
record contains fields of the aforementioned types be sure to drop the file
on the window background, not on the External field The appropriate window
will then appear with the title “Import text file”.

You are strongly advised to use proper CSV files if at all possible.  You
could, in fact, use the filer to set the filetype of such non-standard files
to &dfe (omit the “&”) so that the problem of Powerbase taking the wrong
action doesn’t arise.  Be sure to use Options to set the correct field
separator and record terminator though.

8.4.4   What if the imported data won’t fit?

There are two situations in which this can happen. The database might not
contain enough free records to hold all the imported data and so you get a
“Database full when reading CSV file” error. To avoid this either make sure
the database is big enough before you start or place a suitable value in the
Increment for expansion icon in the Change length window.  The latter is
accessible from the Utilities submenu of the iconbar menu (see 10.5).

The second situation is where an item is too long for the destined database
field. When importing data Powerbase maintains a file called TooBig inside
the database’s PrintJobs directory. Anything which won’t fit in the target
field is instead written to this file together with information about where
it was intended to go and an “@” character is placed in the database field
to draw your attention to it. No writable Powerbase field may be longer than
246 characters and if an item of imported data exceeds this a note will be
made in the TooBig file advising you to define an External field (Text Block
or Text) for such data. After completing a CSV import operation it is
advisable to look at the TooBig file to see if any remedial action is
needed.

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8.5     Using CSV files to modify existing records
--------------------------------------------------
Most database programs which support CSV import allow it to be used only for
creating new records.  Powerbase is unusual in that you can use a CSV file
to modify existing records. This capability should be used with caution
since careless use can irrevocably garble a database.  There are three
relevant radio buttons in the CSV options window. They are called Modify
existing, With primary key and With rec. number and their actions are as
follows:

Modify existing No new records will be created when a CSV file is dropped
onto the record window.  The existing records will be accessed in the order
determined by the current index and the new data will be merged into these
records.  You should, of course, either use ADJUST to highlight the fields
into which the data is to go or place a header in the CSV file specifying
the field tags and then turn on the With header switch (see 8.4.2).  If all
the records are modified before the end of the CSV file has been reached a
warning message is displayed.  Note that it is the user’s responsibility to
ensure that the data in the CSV file is in the correct order since Powerbase
has no way of telling which data is destined for which record and can only
proceed sequentially.  As an additional precaution a warning message is
displayed when you choose this option.

With primary key This affects both export and import.  When you export data
with this button selected  each record of the CSV file includes the primary
key of the Powerbase record. (Try creating a CSV file with and without this
option set and compare the files using Edit.)  When importing such a file
Powerbase will attempt to locate records with the same primary keys as the
records in the CSV file. If a matching key is not found a new record will be
created to receive the data. If the key does exist then the CSV data goes
into the same record, overwriting any data which the target fields already
contain.  The option is only useful for transferring data between Powerbase
databases which have the same primary key field(s) and structure.  Don’t
forget that Powerbase, by default, allows duplicate primary keys so it is
possible for the new data to go into the wrong record.  You would be
ill-advised to trust this method of import unless you are sure each primary
key is unique.

With record number This resembles the previous option. It allows data to be
exported with the Powerbase record numbers included. Importing into another
(or the same) database places the data in records having the same record
numbers, again overwriting data which may already be present in the target
fields.  This option is only useful for transferring data between Powerbase
databases in which corresponding records have identical record numbers.  One
use for it might be to export a set of data, load it into an editor and do
some extensive searching-and-replacing, then put the modified data back into
the original database.

8.6     Creating a new, working database from a CSV file
--------------------------------------------------------
There is an option button in the CSV options window called With field data
which only becomes active when the With header button is selected. With the
switch selected the header record of a saved CSV file contains not only the
field names but also the field lengths and types. Again it is suggested that
you create a file and look at it in Edit. Each item in the header begins
with a number. This is the field length in characters, i.e. the maximum
allowed length in the Powerbase record field. Next comes a ¤ character which

separates the length from the field name. Another ¤ separates the field name
from the concluding number which determines the field type. (The type
numbers may be inspected by looking at the ValStrings file in the Powerbase
directory.)

A file created in this form is not meant to be dropped onto the window of an
open database. It should be dropped onto the Powerbase icon on the iconbar
when no database is open. Powerbase will attempt to convert the file into a
functioning database. All the fields will be ranged on the left of the
record window, one beneath another and the primary key will consist of the
first four characters of the first field. Don’t try to create databases
containing Check box, Button or External fields using this method; it’s only
meant for the most basic type of database in which all fields are of the
Editable class.

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