I have a snippet of PL/SQL code that looks similar to this:
IF l_order = 'Cancelled At Order Stage' OR l_order = 'Stopped at Billing Stage' THEN
Do something
END IF;
IF l_type = 'Internal' OR l_type = 'Contracted' THEN
Do something else
END IF;
I'd like to avoid having the hard coded strings, so I considered a simple array. However, it seems like a lot of extra lines of code (creating a type, creating an array of the type, iterating through that array) just to do what I've got here.
What are the recommendations on what to do here? I know this is a very minimal issue and I'm probably micro optimising, but I'd look to know what good practice is.
$A := Hard-coding
$B := bad
$C := weigh
$D := advantage
$E := configurability
$F := cost
$G := reduced readability
$A is not always $B. You have to $C the $D of $E against the $F of $G.
People can only keep a small number of new variables in their head at once. It's up to you to decide what in your system has meaning. For example, if developers see the phrase "Cancelled At Order Stage" a dozen times a day, reading it requires no thought. If you replace that phrase with C_CANCEL_STATUS your code becomes less readable.
Or maybe you just need a little PL/SQL syntactic sugar. For example, using a pre-defined collection and the member of operator may help simplify things:
declare
c_cancelled_statuses constant sys.dbms_debug_vc2coll :=
sys.dbms_debug_vc2coll('Cancelled At Order Stage', 'Stopped at Billing Stage');
begin
if 'Cancelled At Order Stage' member of c_cancelled_statuses then
dbms_output.put_line('Cancelled!');
end if;
end;
/
All programmers understand that hard-coding can be bad (right?). Hard-coding can hurt your code but probably won't kill it.
But I've seen several systems completely destroyed by softcoding. I know too many managers that think any line of code is "hard-coded", and that all logic should be stored in a configuration table. Many horrible, proprietary programming languages have been built because of a a fear of hard-coding. Don't feel too bad about occasionally hard-coding.
Related
I need a help
I'm make a function in plsql but I'm beginner
Challenge: Web a label has (imput) in less than 72hours it will not be able to leave stock
Could you help me or tell me if I'm on the right path?
create or replace FUNCTION CHECACODENTRADA
(
P_CODPRO IN VARCHAR2
)
RETURN VARCHAR2
AS
v_database DATE;
BEGIN
v_database := TRUNC (SYSDATE);
IF (p_CODPRO == '08932010','08932030','08942020','08942010','08942310','08932210')
THEN
SELECT SYSDATE+3/72 FROM DUAL
IF SYSDATE+3/72 >=
Welcome to stack overflow. I suggest you start by writing a function shell and then adding functionality to it.
create or replace FUNCTION CHECACODENTRADA
(
P_CODPRO IN VARCHAR2
) RETURN VARCHAR2
AS
BEGIN
RETURN 'ok';
END;
/
Then the next step. Add code and compile. Fix any errors and continue. If you're a complete novice then don't write large chunks of code because it could be hard to figure out what is wrong.
How are you creating these functions - are you using a proper tool like sqldeveloper ? If not... well you should. Those tools make developing pl/sql a lot easier.
Read documentation, look for examples. pl/sql has its own syntax, don't assume that you can just borrow the syntax javascript or java uses... that will cause numerous errors. In your code, for example:
-- 2 errors in following line.
-- 1. The "==" is not valid oracle syntax
-- 2. What is this ? '08932010','08932030'... is that a list of arguments - how would the operator "==" handle this ? What are you expecting ?
IF (p_CODPRO == '08932010','08932030','08942020','08942010','08942310','08932210') THEN
-- the code below will not compile. You cannot "just select" in pl/sql, you need to SELECT INTO a variable.
SELECT SYSDATE+3/72 FROM DUAL
Some places you can start:
the source of it all: https://docs.oracle.com/en/database/oracle/oracle-database/18/lnpls/plsql-language-fundamentals.html#GUID-640DB3AA-15AF-4825-BD6C-1D4EB5AB7715
Google "pl/sql basics" and read up on it.
write small blocks in pl/sql to try things out. Use the sample schema emp/dept to have sample data everyone knows. You can get a database schema on apex.oracle.com (well that is an apex workspace but in the sql workshop you can do all the pl/sql you want) or use livesql.oracle.com
Other than that, you wrote your first code and asked questions about it - so you're definitely on the right track :)
In Modula-2 and Oberon each module and procedure declaration must end with the name of the module or procedure. It is not needed in Pascal. I have never really understood the motivation for this. Can someone enlighten me?
After reading some (I am not an expert) I would wager this is just a syntax demand of the function for better readability.
I'll go one step further, and say in large, old, badly written procedures/function in other languages, this is sometimes done without the language requiring it. I've often seen:
int veryLongC++Function() {
...
...
... 3000 code lines
} //veryLongC++Function
So a reader jumping near the end knows what in the mess they are looking at. August mentions in the comment this is much less robust when not enforced by the compiler - in case of a name change.
Another important aspect is nested procedures - here the explicit ending makes things much more readable - checkout chapter 7 for an example - a nested procedure is declared between a declaration and before the BEGIN. The syntax makes this looks much better (in my opinion).
So long story short - I think the main benefit is readability.
It's possible you get something like this:
MODULE A;
...
PROCEDURE B;
...
PROCEDURE C;
...
BEGIN (* C *)
...
END C;
BEGIN (* B *)
...
END B;
BEGIN (* A *)
...
END A.
In that case, for readability you have three bodies (and more if you have defined nested procedures and functions) at the end of your code. In order to see which one is the one ending in the END clause, it's better if the compiler can check that you ar closing things correctly (as you see, I even put it ---as a comment, but would be nice if the compiler accepted it as a valid identifier and checked just to be sure things match correctly--- at the start BEGIN body clause)
Hi everyone I'm new to PL/SQL ,however I'm wrting a small code that a prompt a user to input a 2 numbers and display the numbers using DBMS_output.Put_line .
but I get a compilation error ,below is my code ,I'm using "Oracle SQL developer"
SET SERVEROUTPUT ON SIZE 1000000;
DECLARE
n_no_1 number(8,2);
n_no_2 number(8,2);
BEGIN
DBMS_output.put_line('Enter Value for no 1');
&n_no_1;
DBMS_output.put_line('Enter value for no 2');
&n_no_2;
DBMS_OUTPUT.PUT_LINE('The value of No 1 is' || n_no_1 );
DBMS_OUTPUT.PUT_LINE('The value of No 2 is' || n_no_2 );
END;
/
These 2 lines are your problem, however, not for the reasons mentioned in other answer:
&n_no_1;
&n_no_2;
In SQL, you can use the ampersand (&) to trigger something called "Macro substitution".
When the compiler comes across something like this (ie &n_no1), it prompts the user to input a value for it to substitute in it's place.
So if you enter "Hello". Your code becomes:
DBMS_output.put_line('Enter Value for no 1');
Hello;
And as you can see, that would fail, if you had just typed that out.
What you want to do is to assign that value to a variable, like this:
n_no_1 := '&n_no_1';
That gets "replaced" by this:
n_no_1 := 'Hello';
which compiles - and runs - just fine.
That all said, this is NOT the best way to do this, although this appears to be a learning excercise ?
Look up the PROMPT and ACCEPT keywords .. you can use those in SQL (outside your BEGIN / DECLARE / END block) to capture the values first in a neater fashion :)
http://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_twelve032.htm#SQPUG052
http://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_twelve005.htm#SQPUG026
Found an additional link here worth a good read. Explains a lot more than what you're looking at, but it discusses substitution variables, and other similiar things (and some other unrelated things :) )
https://blogs.oracle.com/opal/entry/sqlplus_101_substitution_varia
The &variable syntax is not PL/SQL: it is part of SQL Developer. I see what you are trying to do and syntax errors, but there's no point in correcting them because it's not going to work in the end.
The reason is: you cannot accept user input via PL/SQL at runtime.
I'm always looking to improve and applying best practices. I read quite a bit about refactoring in the last weeks. I have to work with a lot of awful code and I produced some not so nice stuff too but I'm trying to change that. Thats no problem for most languages but I'm pretty new to PL/SQL so I just copied the style of the already written code.
After reading some tutorials I realized that a lot of our code is pretty much more C style code using retval instead exceptions etc.
We have a lot of functions like open cursor, loop through it, validate the data, trim it or make some string manipulation and insert it into another table, update the status etc. I wonder what a best practice solution would look like on something like this. Atm most functions look like this:
LOOP
FETCH C_ABC INTO R_ABC;
EXIT WHEN C_ABC%NOTFOUND OR C_ABC%NOTFOUND IS NULL;
SAVEPOINT SAVE_LOOP;
retval := plausibilty_check(r_ABC);
IF (retval = STATUS_OK) THEN
retval := convert_ABC_TO_XYZ(r_ABC, r_XYZ);
END IF;
IF (retval = STATUS_OK) THEN
retval := insert_XYZ(r_XYZ);
END IF;
retval := update_ABC(r_ABC.PK_Id, retval);
END LOOP;
If i was using exceptions I guess I had to raise them inside the functions so I can handle them in the main function, if not everyone would have to crawl to every sub function to understand the program and where the updates happen etc. So I guess I would have to use another PL/SQL block inside the loop? Like:
LOOP
FETCH C_ABC INTO R_ABC;
EXIT WHEN C_ABC%NOTFOUND OR C_ABC%NOTFOUND IS NULL;
SAVEPOINT SAVE_LOOP;
BEGIN
plausibilty_check(r_ABC);
convert_ABC_TO_XYZ(r_ABC, r_XYZ);
insert_XYZ(r_XYZ);
update_ABC(r_ABC.PK_Id, STATUS_OK);
EXCEPTION
WHEN ERROR_CODE_XYZ THEN
update_ABC(r_ABC.PK_Id, ERROR_CODE_XYZ);
END
END LOOP;
I guess that function handles a pretty common problem but I still havn't found any tutorial covering something like this. Maybe someone more experienced with PL/SQL might gimme a hint what a best practice on a task like that would look like.
I like to use exceptions to jump out of a block of code if an exceptional event (e.g. an error) occurs.
The problem with the "retval" method of detecting error conditions is that it introduces a second layer of semantics on what a function is and for.
In principle, a function should be used to perform a calculation and return a result; in this sense, a function doesn't do anything, i.e. it makes no changes to any state - it merely returns a value.
If it cannot for some reason calculate that value, that would be an exceptional circumstance, so I'd want the function to raise an exception so that the calling program will not blindly continue on its merry way, thinking it got a valid value from the function.
On the other hand, a procedure is a method by which action is done - something is changed, something is validated, or something is sent. The normal expected path is that the procedure is executed, it does its thing, then it finishes. If an error occurs, I want it to raise an exception so that the calling program will not blindly continue thinking that the procedure has successfully done its thing.
Thus, the original intent of the fundamental difference between "procedures" and "functions" is preserved.
In languages like C, there are no procedures - everything is a function in a sense (even functions that return "void") - but in addition, there is no real concept of an "exception" - so these semantics don't apply. It's for this reason that the C style of returning an error/success flag don't translate well into languages like PL/SQL.
In your example, I'd consider doing it something like this:
BEGIN
LOOP
FETCH c_ABC INTO r_ABC;
EXIT WHEN c_ABC%NOTFOUND;
IF record_is_plausible(r_ABC) THEN
r_XYZ := convert_ABC_TO_XYZ(r_ABC);
insert_or_update_XYZ(r_XYZ);
ELSE
update_as_implausible(r_ABC);
END IF;
END LOOP;
EXCEPTION
WHEN OTHERS THEN
-- log the error or something, then:
RAISE;
END;
So where the semantics of the operation is doing some validation or something, and returning a result, I converted plausibilty_check into a function record_is_plausible that returns a boolean.
I'd pull the call to update_ABC out of the BEGIN block and make it common at the bottom of the loop, as in:
DECLARE
nFinal_status NUMBER;
BEGIN
LOOP
FETCH C_ABC INTO R_ABC;
EXIT WHEN C_ABC%NOTFOUND OR C_ABC%NOTFOUND IS NULL;
SAVEPOINT SAVE_LOOP;
nFinal_status := nSTATUS_OK;
BEGIN
plausibilty_check(r_ABC);
convert_ABC_TO_XYZ(r_ABC, r_XYZ);
insert_XYZ(r_XYZ);
EXCEPTION
WHEN excpERROR_CODE_XYZ THEN
nFinal_status := nERROR_CODE_XYZ;
END;
update_ABC(r_ABC.PK_Id, nFinal_status);
END LOOP;
END;
You might want to have each of the procedures throw its own exception so you could more easily identify where the issue(s) are coming from - or use different exceptions/error codes for each possible issue (for example, the plausibility check might raise different exceptions depending on what implausible condition it found). However, in my experience plausibility checks will often uncover multiple conditions (if the data's bad it's often really bad :-), so it might be nice to tabularize the errors and relate them to the base ABC data through a foreign key, thus allowing each individual error to be identified with just one pass through the data. Then the 'status' field on ABC becomes moot; you either have errors associated with the ABC row or you don't. If errors exist, do whatever is needed. If no errors, proceed with 'normal' processing.
Just a thought.
Share and enjoy.
I have a lot of data that I need to sort through and one of the fields contains both the make/model of the vehicle as well as the reg, sometimes separated by a dash (-) sometimes however it is not. Here is an example of such a string:
VehicleModel - TU69YUP
VehicleModel - TU69 YUP
VehicleModel TU69YUP
VehicleModel TU69 YUP
There are also some other variations but they are the main ones I have encountered. Is there a way that I can reliably go through all of the data and separate the vehicle reg from the model?
The data is currently contained within a Paradox database which I have no problem going through. I do not have a list of all of the vehicle models and names that are contained within the database, likewise, I also do not have a list of the licence plates.
The project is written in Delphi/SQL so I would prefer to stick with either one of these if at all possible.
Trouble ahead
If that field was originally entered by a user in the form that you're now seeing, then we can assume there was no validation, the original program would simply store whatever the user entered. If that's the case, you can't get 100% accuracy: human beings will always make mistakes, intentionally or unintentionally. Expect this kinds of human errors:
Missing fields (ie: registration only, no vehicle information - or the other way around)
Meaningless duplication of words (example: "Ford Ford K - TU 69 YUP")
Missing letters, duplicated letters, extra garbage letters. Example: "For K - T69YUP"
Wrong order of fields
Other small errors you can't even dream of.
Plain garbage that not even a human would make sense of.
You might have guessed I'm a bit pessimistic when dealing with human-entered data straight into text fields. I had the distinct misfortune to deal with a database where all data was text and there was no validation: Can you guess the kind of nonsense people typed in unvalidated date fields that allowed free user input?
The plan
Things aren't as dark as they seem, you can probably "fix" lots of things. The trick here is making sure you only fix data that's unambiguous and let a human sift through the rest of the stuff. The easiest way to do that is to do something like this:
Look at the data you have and wasn't automatically fixed yet. Figure out a rule that unambiguously applies to lots of records.
Apply the unambiguous rule.
Repeat until only a few records are left. Those should be fixed by hand, because they resisted all automatic methods that were applied.
The implementation
I strongly recommend using regular expressions for all the tests, because you'll surely end up implementing lots of different tests, and regular expressions can easily "express" the slight variations in search text. For example the following reg-ex can parse all 4 of your examples and give the correct result:
(.*?)(\ {1,3}-\ {1,3})?(\b[A-Z]{2}\ {0,2}[0-9]{2}\ {0,3}[A-Z]{3}\b)
If you've never worked with regular expressions before, that single expressions looks unintelligible, but it's in fact very simple. This is not a reg-ex question so I'm not going into any details. I'd rather explain how I've come up with the idea.
First of all, if the text includes vehicle registration numbers, those numbers will be in a very strict format: they'd be easy to match. Given your example I assume all registration numbers are of the form:
LLNNLLL
where "L" is a letter and "N" is a number. My regex is rigid in it's interpretation of it: it wants exactly two uppercase letters, followed by a small number of spaces (or no space), followed by exactly two digits, followed by a small number of spaces (or no space), finally followed by exactly 3 uppercase letters. The part of the regex that deals with that is:
[A-Z]{2}\ {0,2}[0-9]{2}\ {0,3}[A-Z]{3}
The rest of the regex makes sure the registration number isn't found embedded into other words, deals with grouping text into capture groups and creates an "lazy capture group" for the VehicleModel.
If I were to implement this myself, I'd probably write a "master" function and a number of simpler "case" functions, each function dealing with one kind of variation in user input. Example:
// This function does a validation of the extracted data. For example it validates the
// Registration number, using other, more precise criteria. The parameters are VAR so the
// function may normalize the results.
function ResultsAreValid(var Make, Registration:string): Boolean;
begin
Result := True; // Only you know what your data looks like and how it can be validated.
end;
// This is a case function that deals with a very rigid interpretation of user data
function VeryStrictInterpretation(const Text:string; out Make, Registration: string): Boolean;
var TestMake, TestReg: string;
// regex engine ...
begin
Result := False;
if (your condition) then
if ResultsAreValid(TestMake, TestReg) then
begin
Make := TestMake;
Registration := TestReg;
Result := True;
end;
end;
// Master function calling many different implementations that each deal with all sorts
// of variations of input. The most strict function should be first:
function MasterTest(const Text:string; out Make, Registration: string): Boolean;
begin
Result := VeryStrictInterpretation(Text, Make, Registration);
if not Result then Result := SomeOtherImplementation(Text, Make, Registration);
if not Result then Result := ThirdInterpretation(Text, Make, Registration);
end;
The idea here is to try to make multiple SIMPLE procedures, that each understands one kind of input in an unambiguous way; And make sure each step doesn't return false positives! And finally don't forget, a human should deal with the last few cases, so don't aim for a fix-it-all solution.
Well assuming that they are of the same format. Word[space]Word
Then you can iterate through them all, and if you encounter a whitespace without a dash, insert a dash. Then split as normal.
Here is a code example.
It will check for the - and also remove possible spaces in the license number.
Note : (as commented by Ken White), if the vehicle contains a space, this will have to be handled as well.
type
EMySplitError = class(Exception);
procedure SplitVehicleAndLicense( s : String; var vehicle,license : String);
var
p : Integer;
begin
vehicle := '';
license := '';
p := Pos('-',s);
if (p = 0) then
begin // No split delimiter
p := Pos(' ',s);
if (p > 0) then
begin
vehicle := Trim(Copy(s,1,p-1));
license := Trim(Copy(s,p+1,Length(s)));
end
else
Raise EMySplitError.CreateFmt('Not a valid vehicle/license name:%s',[s]);
end
else
begin
vehicle := Trim(Copy( s,1,p-1));
license := Trim(Copy( s,p+1,Length(s)));
end;
// Trim spaces in license
repeat
p := Pos(' ',license);
if (p <> 0) then Delete(license,p,1);
until (p = 0);
end;