I tried to match the sql values string (0),(5),(12),... or (0,11),(122,33),(4,51),... or (0,121,12),(31,4,5),(26,227,38),... and so on with the regular expression
\(\s*\d+\s*(\s*,\s*\d+\s*)*\)(\s*,\s*\(\s*\d+\s*(\s*,\s*\d+\s*)*\))*
and it works. But...
How can I ensure that the regex does not match a values string like (0,12),(1,2,3),(56,7) with different number of columns?
Thanks in advance...
As i mentioned in comment to the question, the best way to check if input string is valid: contains the same count of numbers between brackets, is to use client side programm, but not clear SQL.
Implementation:
List<string> s = new List<string>(){
"(0),(5),(12)", "(0,11),(122,33),(4,51)",
"(0,121,12),(31,4,5),(26,227,38)","(0,12),(1,2,3),(56,7)"};
var qry = s.Select(a=>new
{
orig = a,
newst = a.Split(new string[]{"),(", "(", ")"},
StringSplitOptions.RemoveEmptyEntries)
})
.Select(a=>new
{
orig = a.orig,
isValid = (a.newst
.Sum(b=>b.Split(new char[]{','},
StringSplitOptions.RemoveEmptyEntries).Count()) %
a.newst.Count()) ==0
});
Result:
orig isValid
(0),(5),(12) True
(0,11),(122,33),(4,51) True
(0,121,12),(31,4,5),(26,227,38) True
(0,12),(1,2,3),(56,7) False
Note: The second Select statement gets the modulo of sum of comma instances and the count of items in string array returned by Split function. If the result isn't equal to zero, it means that input string is invalid.
I strongly believe there's a simplest way to achieve that, but - at this moment - i don't know how ;)
:(
Unless you add some more constraints, I don't think you can solve this problem only with regular expressions.
It isn't able to solve all of your string problems, just as it cannot be used to check that the opening and closing of brackets (like "((())()(()(())))") is invalid. That's a more complicated issue.
That's what I learnt in class :P If someone knows a way then that'd be sweet!
I'm sorry, I spent a bit of time looking into how we could turn this string into an array and do more work to it with SQL but built in functionality is lacking and the solution would end up being very hacky.
I'd recommend trying to handle this situation differently as large scale string computation isn't the best way to go if your database is to gradually fill up.
A combination of client and serverside validation can be used to help prevent bad data (like the ones with more numbers) from getting into the database.
If you need to keep those numbers then you could rework your schema to include some metadata which you can use in your queries, like how many numbers there are and whether it all matches nicely. This information can be computed inexpensively from your server and provided to the database.
Good luck!
Related
I'm hoping someone can help answer my question, perhaps with an idea of where to go or whether what I'm trying to do is not possible with the way I want to do it.
I've been asked to write a set of rules based on the data held by our ERP form components or variables.
Unfortunately, these components and variables cannot be accessed or used outside of the ERP, so I can't use SQL to query the values and then build some kind of SQL query.
They'd like the ability to put statements like these:
C(MyComponentName) = C(MyOtherComponentName)
V(MyVariableName) > 16
(C(MyComponentName) = "") AND V(MyVariableName) <> "")
((C(MyComponentName) = "") OR C(MyOtherComponentName) = "") AND V(MyVariableName) <> "")
This should be turned into some kind of query which gets the value of MyComponentName and MyOtherComponentName and (in this case) compares them for equality.
They don't necessarily want to just compare for equality, but to be able to determine whether a component / variable value is greaterthan or lessthan etc.
Basically it's a free-form statement that gets converted into something similar to an IF statement.
I've tried this:
Sub TestCondition()
Dim Condition as string = String.Format("{0} = {1}", _
Component("MyComponent").Value, Component("MyOtherComponent").Value)
If (Condition) Then
' Do Something
Else
' Do Something Else
End If
End Sub
Obviously, this does not work and I honestly didn't think it would be so simple.
Ignoring the fact that I'd have to parse the line, extract the required operators, the values from components or variables (denoted by a C or V) - how can I do this?
I've looked at Expression Trees but these were confusing, especially as I'd never heard of them, let alone used them. (Is it possible to create an expression tree for dynamic if statements? - This link provided some detail on expression trees in C#)
I know an easier way to solve this might be to simply populate the form with a multitude of drop-down lists, so users pick what they want from lists or fill in a text box for a specific search criteria.
This wouldn't be a simple matter as the ERP doesn't allow you to dynamically create controls on its forms. You have to drag each component manually and would be next to useless as we'd potentially want at least 1 rule for every form we have (100+).
I'm either looking for someone to say you cannot do this the way you want to do it (with a suitable reason or suggestion as to how I could do it) that I can take to my manager or some hints, perhaps a link or 2 pointing me in the right direction.
If (Condition) Then
This is not possible. There is no way to treat data stored in a string as code. While the above statement is valid, it won't and can't function the way you want it to. Instead, Condition will be evaluated as what it is: a string. (Anything that doesn't boil down to 0 is treated as True; see this question.)
What you are attempting borders on allowing the user to type code dynamically to get a result. I won't say this is impossible per se in VB.Net, but it is incredibly ambitious.
Instead, I would suggest clearly defining what your application can and can't do. Enumerate the operators your code will allow and build code to support each directly. For example:
Public Function TestCondition(value1 As Object, value2 As Object, op as string) As Boolean
Select Case op
Case "="
Return value1 = value2
Case "<"
Return value1 < value2
Case ">"
Return value1 > value2
Case Else
'Error handling
End Select
End Function
Obviously you would need to tailor the above to the types of variables you will be handling and your other specific needs, but this approach should give you a workable solution.
For my particular requirements, using the NCalc library has enabled me to do most of what I was looking to do. Easy to work with and the documentation is quite extensive - lots of examples too.
I need to store an alphanumeric string in an integer column on one of my models.
I have tried:
#result.each do |i|
hex_id = []
i["id"].split(//).each{|c| hex_id.push(c.hex)}
hex_id = hex_id.join
...
Model.create(:origin_id => hex_id)
...
end
When I run this in the console using puts hex_id in place of the create line, it returns the correct values, however the above code results in the origin_id being set to "2147483647" for every instance. An example string input is "t6gnk3pp86gg4sboh5oin5vr40" so that doesn't make any sense to me.
Can anyone tell me what is going wrong here or suggest a better way to store a string like the aforementioned example as a unique integer?
Thanks.
Answering by request form OP
It seems that the hex_id.join operation does not concatenate strings in this case but instead sums or performs binary complement of the hex values. The issue could also be that hex_id is an array of hex-es rather than a string, or char array. Nevertheless, what seems to happen is reaching the maximum positive value for the integer type 2147483647. Still, I was unable to find any documented effects on array.join applied on a hex array, it appears it is not concatenation of the elements.
On the other hand, the desired result 060003008600401100500050040 is too large to be recorded as an integer either. A better approach would be to keep it as a string, or use different algorithm for producing a number form the original string. Perhaps aggregating the hex values by an arithmetic operation will do better than join ?
This is an ugly one. I wish I wasn't having to ask this question, but the project is already built such that we are handling heavy loads of validations in the database. Essentially, I'm trying to build a function that will take two stacks of data, weave them together with an unknown batch of operations or comparators, and produce a long string.
Yes, that was phrased very poorly, so I'm going to give an example. I have a form that can have multiple iterations of itself. For some reason, the system wants to know if the entered start date on any of these forms is equal to the entered end date on any of these forms. Unfortunately, due to the way the system is designed, everything is stored as a string, so I have to format it as a date first, before I can compare. Below is pseudo code, so please don't correct me on my syntax
Input data:
'logFormValidation("to_date(#) == to_date(^)"
, formname.control1name, formname.control2name)'
Now, as I mentioned, there are multiple iterations of this form, and I need to loop build a fully recursive comparison (note: it may not always be typical boolean comparisons, it could be internally called functions as well, so .In or anything like that won't work.) In the end, I need to get it into a format like below so the validation parser can read it.
OR(to_date(formname.control1name.1) == to_date(formname.control2name.1)
,to_date(formname.control1name.2) == to_date(formname.control2name.1)
,to_date(formname.control1name.3) == to_date(formname.control2name.1)
,to_date(formname.control1name.1) == to_date(formname.control2name.2)
:
:
,to_date(formname.control1name.n) == to_date(formname.control2name.n))
Yeah, it's ugly...but given the way our validation parser works, I don't have much of a choice. Any input on how this might be accomplished? I'm hoping for something more efficient than a double recursive loop, but don't have any ideas beyond that
Okay, seeing as my question is apparently terribly unclear, I'm going to add some more info. I don't know what comparison I will be performing on the items, I'm just trying to reformat the data into something useable for ANY given function. If I were to do this outside the database, it'd look something like this. Note: Pseudocode. '#' is the place marker in a function for vals1, '^' is a place marker for vals2.
function dynamicRecursiveValidation(string functionStr, strArray vals1, strArray vals2){
string finalFunction = "OR("
foreach(i in vals1){
foreach(j in vals2){
finalFunction += functionStr.replace('#', i).replace('^', j) + ",";
}
}
finalFunction.substring(0, finalFunction.length - 1); //to remove last comma
finalFunction += ")";
return finalFunction;
}
That is all I'm trying to accomplish. Take any given comparator and two arrays, and create a string that contains every possible combination. Given the substitution characters I listed above, below is a list of possible added operations
# > ^
to_date(#) == to_date(^)
someFunction(#, ^)
# * 2 - 3 <= ^ / 4
All I'm trying to do is produce the string that I will later execute, and I'm trying to do it without having to kill the server in a recursive loop
I don't have a solution code for this but you can algorithmically do the following
Create a temp table (start_date, end_date, formid) and populate it with every date from any existing form
Get the start_date from the form and simply:
SELECT end_date, form_id FROM temp_table WHERE end_date = <start date to check>
For the reverse
SELECT start_date, form_id FROM temp_table WHERE start_date = <end date to check>
If the database is available why not let it do all the heavy lifting.
I ended up performing a cross product of the data, and looping through the results. It wasn't the sort of solution I really wanted, but it worked.
Quick question. I'm in a bit of a rush but if someone could quickly point me in the right direction I would be very very happy.
I have a field in the db, let's call it field_a which returns a string in the format "20,50,60,80" etc.
I wish to do a query which will search in this field to see if 20 exists.
Could I use MySQL MATCH or is there a better way?
Thank you!
The better way would be to save the data differently. With WHERE a LIKE '...' and MATCH/AGAINST (besides being fairly slow) you can't easily search for just "20"... If you search for "20" you'll get "200" too; if you search for ",20," you won't get "20, 50"
Use FIND_IN_SET:
WHERE FIND_IN_SET(20, field_a) != 0
Just be careful you don't get a substring of what you actually want - for example LIKE '%20%' would also match '50,120,70'. If you're using MySQL, you might want to use REGEXP '[[:<:]]20[[:>:]]' - where the funny faces are word boundary markers that will respect break on beginning / end of string or commas so you shouldn't get any false positives.
http://dev.mysql.com/doc/refman/5.1/en/regexp.html
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
String vs StringBuilder
I just revisited some of the books that I used to pick up VB.NET. I am not sure I've got this in my head, understand how/what StringBuilder is.
What is the guidance for using? Is it best to use it if you are are concatenating 2 strings or 50?
Or when the the total string length is greater than 128 characters?
Or will you see a performance benefit whenever you use it to add strings together?
In which case is it better to use a StringBuilder instance to build a SQL statement than string.format("Select * from x where y = {0}",1)?
It's always struck me that declaring another variable and including a name space is not beneficial for small string concatenations, but I am not sure now.
Sorry, lot of documentation tells you what to use, just not what's best.
I've got an article on this very topic. In summary (copied from the bottom of the page):
Definitely use StringBuilder when you're concatenating in a non-trivial loop - especially if you don't know for sure (at compile time) how many iterations you'll make through the loop. For example, reading a file a character at a time, building up a string as you go using the += operator is potentially performance suicide.
Definitely use the concatenation operator when you can (readably) specify everything which needs to be concatenated in one statement. (If you have an array of things to concatenate, consider calling String.Concat explicitly - or String.Join if you need a delimiter.)
Don't be afraid to break literals up into several concatenated bits - the result will be the same. You can aid readability by breaking a long literal into several lines, for instance, with no harm to performance.
If you need the intermediate results of the concatenation for something other than feeding the next iteration of concatenation, StringBuilder isn't going to help you. For instance, if you build up a full name from a first name and a last name, and then add a third piece of information (the nickname, maybe) to the end, you'll only benefit from using StringBuilder if you don't need the (first name + last name) string for other purpose (as we do in the example which creates a Person object).
If you just have a few concatenations to do, and you really want to do them in separate statements, it doesn't really matter which way you go. Which way is more efficient will depend on the number of concatenations the sizes of string involved, and what order they're concatenated in. If you really believe that piece of code to be a performance bottleneck, profile or benchmark it both ways.
Here is my rule of thumb:
StringBuilder is best used when the exact number of concatenations is unknown at compile time.
Coding Horror has a good article concerning this question, The Sad Tragedy of Micro-Optimization Theater.
Personally I use StringBuilder when I have more than just one or two strings to concatenate. I'm not sure if there's a real performance hit to be gained, but I've always read and been told that doing a regular concatenation with multiple strings creates an extra copy of the string each time you do it, while using StringBuilder keeps one copy until you call the final ToString() method on it.
Someone's figured out experimentally that the critical number is 6. More than 6 concatenations in a row and you should use a StringBuilder. Can't remember where I found this.
However, note that if you just write this in a line:
"qwert" + "yuiop" + "asdf" + "gh" + "jkl;" + "zxcv" + "bnm" + ",."
That gets converted into one function call (I don't know how to write it in VB.net)
String.Concat("qwert", "yuiop", "asdf", "gh", "jkl;", "zxcv", "bnm", ",.");
So if you're doing all concatenations on one line, then don't bother with StringBuilder because String.Concat effectively will do all the concatenations in one go. It's only if you're doing them in a loop or successively concatenating.
My rule - when you're adding to a string in a For or Foreach loop, use the StringBuilder.