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You can use OPL to create data files (databases) like those used by the Data application. You can store any kind of information in a data file, and retrieve it for display, editing or calculations.
This chapter covers:
The Series 5 and the Series 3c database models differ quite substantially. However, the Series 3c method of database programming (except for some removed keywords as indicated) is completely understood by the Series 5 model and any existing code will not have to change. However, it is very strongly recommended that, on the Series 5 you use the new keywords INSERT, MODIFY, PUT and CANCEL, along with bookmarks and transactions, rather than using APPEND, UPDATE, POS and POSITION.
If you are using the Series 5, it is recommended that you should read this chapter for a description of simple database use, and then the following chapter which refers specifically to features available on the Series 5.
Data files (or databases) are made up of records which contain data in each of their fields. For example, in a database of names and addresses, each record might have a name field, a telephone number field, and separate fields for each line of the address.
In OPL you can:
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Use the CREATE command like this:
CREATE filename$,logical name,field1,field2,...
For example:
CREATE "clients",B,nm$,tel$,ad1$,ad2$,ad3$
creates a data file called clients.
The file name is a string, so remember to put quote marks around it. You can also assign the name string to a string variable (for example fil$="clients") and then use the variable name as the argument - CREATE fil$,A,field1,field2.
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You can have up to 26 data files open at a time. Each of these must have a logical name: A to Z. |
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You can have up to 4 data files open at a time. Each of these must have a logical name: A, B, C or D. |
The logical name lets you refer to this file without having to keep using the full file name.
A different logical name must be used for each data file opened - e.g. one called A, one called B and one called C. A file does not have to be opened with the same logical name as the last time it was opened. When a file is closed, its logical name is freed for use by another file.
field1, field2,... are the field names - up to 32 in any record. These are like variables, so - use % & or $ to make the appropriate types of fields for your data. You cannot use arrays. Do not specify the maximum length of strings that the string fields can handle. The length is automatically set at 255 characters.
Field names may be up to 8 characters long, including any qualifier like &.
When referring to fields, add the logical file name to the front of the field name, to specify which opened file the fields belong to. Separate the two by a dot. For example, A.name$ is the name$ field of the file with logical name A, and C.age% is the age% field of the file with logical name C.
The values of all the fields are 0 or null to start with. You can see this if you run this example program:
PROC creatfil:
CREATE "example",A,int%,long&,float,str$
PRINT "integer=";a.int%
PRINT "long=";a.long&
PRINT "float=";a.float
PRINT "string=";a.str$
CLOSE
GET
ENDP
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When you first CREATE a data file it is automatically open, but it closes again when the program ends. If a file already exists, trying to CREATE it again will give an error - so if you ran the procedure creatfil: a second time you would get an error. To open an existing file, use the OPEN command.
OPEN works in the same way as the CREATE command. For example:
OPEN "clients",B,nm$,tel$,ad1$,ad2$,ad3$
You might make a new module, and type these two procedures into it:
PROC openfile:
IF NOT EXIST("example")
CREATE "example",A,int%,lng&,fp,str$
ELSE
OPEN "example",A,int%,lng&,fp,str$
ENDIF
PRINT "Current values:"
show:
PRINT "Assigning values"
A.int%=1
A.lng&=&2**20 REM the 1st & avoids integer overflow
A.fp=SIN(PI/6)
PRINT "Give a value for the string:"
INPUT A.str$
PRINT "New values:"
show:
ENDP
PROC show:
PRINT "integer=";A.int%
PRINT "long=";A.lng&
PRINT "float=";A.fp
PRINT "string=";A.str$
GET
ENDP
The IF...ENDIF checks to see if the file already exists, using the EXIST function. If it does, the file is opened; if it doesn’t, the file is created.
The fields can be assigned values just like variables. The field name must be used with the logical file name like this: A.f%=1 or INPUT A.f$.
If you try to give the wrong type of value to a field (for example "Davis" to f%) an error message will be displayed.
You can access the fields from other procedures, just like global variables. Here the called procedure show: displays the values of the fields.
You must know the type of each field, and you must give each a separate name - you cannot refer to the fields in any indexed way, e.g. as an array.
The OPENR command works in exactly the same way as OPEN, except that the file cannot be written to (with UPDATE or APPEND), only read. However, more than one running program can then look at the file at the same time.
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The last example procedure did not actually save the field values as a record to a file. To do this you need to use the APPEND command. This program, for example, allows you to add records to the example data file:
PROC count:
LOCAL reply%
OPEN "example",A,f%,f&,f,f$
DO
CLS
AT 20,1 :PRINT "Record count=";COUNT
AT 9,5 :PRINT "(A)dd a record"
AT 9,7 :PRINT "(Q)uit"
reply%=GET
IF reply%=%q OR reply%=%Q
BREAK
ELSEIF reply%=%A OR reply%=%a
add:
ELSE
BEEP 16,250
ENDIF
UNTIL 0
ENDP
PROC add:
CLS
PRINT "Enter integer field:";
INPUT A.f%
PRINT "Enter long integer field:";
INPUT A.f&
PRINT "Enter numeric field:";
INPUT A.f
PRINT "Enter string field:";
INPUT A.f$
APPEND
ENDP
The BEEP command makes a beep of varying pitch and length:
BEEP duration%,pitch%
The duration is measured in 1/32 of a second, so duration%=32 would give a beep a second long. Try pitch%=50 for a high beep, or 500 for a low beep.
The COUNT function returns the number of records in the file. If you use it just after creating a database, it will return 0. As you add records the count increases.
Use the APPEND command to save a new record. This has no arguments. The values assigned to A.f%, A.f&, A.f and A.f$ are added as a new record to the end of the example data file. If you only give values to some of the fields, not all, you won’t see any error message. If the fields happen to have values, these will be used; otherwise - null strings ("") will be given to string fields, and zero to numeric fields.
New field values are always added to the end of the current data file - as the last record in the file (if the file is a new one, it will also be the first record).
At any time while a data file is open, the field names currently in use can be used like any other variable - for example, in a PRINT statement, or a string or numeric expression.
APPEND adds the current field values to the end of the file as a new record, whereas UPDATE deletes the current record and adds the current field values to the end of the file as a new record.
When you open or create a file, the first record in the file is current. To read, edit, or erase another record, you must make that record current - that is, move to it. Only one record is current at a time. To change the current record, use one of these commands:
ERASE deletes the current record in the current file.
The next record is then current. If the erased record was the last record in a file, then following this command the current record will be empty and EOF will return true.
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FIND makes current the next record which has a field matching your search string. Capitals and lower-case letters match. For example:
r%=FIND("Brown")
would select the first record containing a string field with the value "Brown", "brown" or "BROWN", etc. The number of that record is returned, in this case to the variable r%. If the number returned is zero, no matching field was found. Any other number means that a match was found.
The search includes the current record. So after finding a matching record, you need to use NEXT before you can continue searching through the following records.
FIND("Brown") would not find a field "Mr Brown". To find this, use wildcards, as explained below.
You can only search string fields, not number fields. For example, if you assigned the value 71 to the field a%, you could not find this with FIND. But if you assigned the value "71" to a$, you could find this.
r%=FIND("*Brown*") would make current the next record containing a string field in which Brown occurred - for example, the fields "MR BROWN", "Brown A.R." and "Browns Plumbing" would be matched. The wildcards you can use are:
? matches any one character
* matches any number of characters.
Once you’ve found a matching record, you might display it on the screen, erase it or edit it. For example, to display all the records containing "BROWN":
FIRST
WHILE FIND("*BROWN*")
PRINT a.name$,a.phone$
NEXT
GET
ENDWH
FINDFIELD, like FIND, finds a string, makes the record with this string the current record, and returns the number of this record. However you can also use it to do case-dependent searching, to search backwards through the file, to search from the first record (forwards) or from the last record (backwards), and to search in one or more fields.
f%=FINDFIELD(a$,start%,no%,flag%)
searches for the string a$ in no% fields in each record, starting at the field with number start% (1 is the number of the first field). start% and no% may refer to string fields only and other types will be ignored. The flag% argument specifies the type of search as explained below. If you want to search in all fields, use 1 as the second argument and for the third argument use the number of fields you used in the OPEN/CREATE command.
flag% should be specified as follows:
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search direction |
flag% |
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backwards from current record |
0 |
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forwards from current record |
1 |
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backwards from end of file |
2 |
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forwards from start of file |
3 |
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Constants for these flags are supplied in Const.oph. See the ‘Calling Procedures’ chapter for details of how to use this file and see Appendix E for a listing of it. |
Add 16 to the value of flag% given above to make the search case-dependent, where case-dependent means that the record will exactly match the search string in case as well as characters. Other wise the search will case-independent which means that upper case and lower case characters will match.
For example, if the following OPEN (or CREATE) statement had been used:
OPEN "clients",B,nm$,tel$,ad1$,ad2$,ad3$
then the command
r%=FINDFIELD("*Brown*",1,3,16)
will search the nm$, tel$ and ad1$ fields of each record for strings containing "Brown" searching case-dependently backwards from the current record.
If you find a matching record and then you want to search again from this record, you must first use NEXT or BACK (according to the direction in which you are searching) to move past the record you have just found, otherwise the search will find the same match in the current record again.
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Immediately after a file has been created or opened, it is automatically current. This means that the APPEND or UPDATE commands save records to this file, and the record-position commands (explained below) move around this file. You can still use the fields of other open files, for example A.field1=B.field2
USE makes current one of the other opened files. For example USE B selects the file with the logical name B (as specified in the OPEN or CREATE command which opened it).
If you attempt to USE a file which has not yet been opened or created, an error is reported.
In this procedure, the EOF function checks whether you are at the end of the current data file — that is, whether you’ve gone past the last record. You can use EOF in the test condition of a loop UNTIL EOF or WHILE NOT EOF in order to carry out a set of actions on all the records in a file.
PROC copyrec:
OPEN "example",A,f%,f&,f,f$
TRAP DELETE "temp" REM If file doesn’t exist, ignore error
CREATE "temp",B,f%,f&,f,f$
PRINT "Copying EXAMPLE to TEMP"
USE A REM the EXAMPLE file
DO
IF a.f%>30 and a.f<3.1415
b.f%=a.f%
b.f&=a.f&
b.f=a.f
b.f$="Selective copy"
USE B REM the TEMP file
APPEND
USE A
ENDIF
NEXT
UNTIL EOF REM until End Of File
CLOSE REM closes A; B becomes current
CLOSE REM closes B
ENDP
This example uses the DELETE command to delete any temp file which may exist, before making it afresh. Normally, if there were no temp file and you tried to delete it, an error would be generated. However, this example uses TRAP with the DELETE command. TRAP followed by a command means "if an error occurs in the command, carry on regardless". The error value can then be found using ERR.
There are more details of ERR and TRAP in the ‘Error Handling’ chapter.
You should always ‘close’ a data file (with the CLOSE command) when you have finished using it. Data files close automatically when programs end.
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You can use up to 26 logical names (files or views — see the ‘Series 5 Data Handling’ chapter) at a time - if you are using 26 logical names and you want to use another one, you must close one of the open files or views first. CLOSE closes the file or view referred to by the current logical name. |
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You can only have 4 files open at a time - if you already have 4 files open and you want to access another one, you must close one of the open files first. CLOSE closes the current file. |
When you change or delete records in a data file, the space taken by the old information is not automatically recovered.
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By default, the space is not recovered when you close the file, unless you have used the SETFLAGS command to enable auto-compaction on closing a file. |
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By default, the space is recovered when you close the file, provided it is on ‘Internal drive’ or on a RAM SSD (i.e. it is not on a Flash SSD). |
Closing a very large file which contains changed or deleted records can be slow when compression is enabled, as the whole file beyond each old record needs copying down, each time.
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You can prevent data file compression on the Series 3c if you wish, with these two lines: |
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On the Series 5, you can use the COMPACT command when the database is closed. See the ‘Series 5 Database Handling’ chapter. |
The files you use with the Data application (listed under the Data icon in the System screen) often called databases or database files - are also just data files.
Data files created by the Data application can be viewed in OPL, and vice versa.
In OPL: to open a data file made by the Data application, begin its name with /DAT/, and end it with .DBF. For example, to open the file called data which the Data application normally uses:
OPEN "/dat/data.dbf",A,a$,b$,c$,d$...
Restrictions:
In the Data application: to examine an OPL data file, press the Data button, select ‘Open file’ from the ‘File’ menu and Control+Tab to type in a file name, and then type the name with /OPD/ on the front and .ODB at the end for example:
/opd/example.odb
Restrictions:
In both cases, you are using a more complete file specification. There is more about file specifications in the ‘Advanced Topics’ chapter.
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For details of using Data application files in OPL on the Series 5, see the next chapter. |
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Be careful to enter these lines exactly as shown. These examples work by setting a system configuration flag.