My client is making database searches using a django webapp that I've written. The query sends a regex search to the database and outputs the results.
Because the regex searches can be pretty long and unintuitive, the client has asked for certain custom "wildcards" to be created for the regex searches. For example.
Ω := [^aeiou] (all non-vowels)
etc.
This could be achieved with a simple permanent string substitution in the query, something like
query = query.replace("Ω", "[^aeiou]")
for all the elements in the substitution list. This seems like it should be safe, but I'm not really sure.
He has also asked that it be possible for the user to define custom wildcards for their searches on the fly. So that there would be some other input box where a user could define
∫ := some other regex
And to store them you might create a model
class RegexWildcard(models.Model):
symbol = ...
replacement = ...
I'm personally a bit wary of this, because it does not seem to add a whole lot of functionality, but does seem to add a lot of complexity and potential problems to the code. Clients can now write their queries to a db. Can they overwrite each other's symbols?
That I haven't seen this done anywhere before also makes me kind of wary of the idea.
Is this possible? Desirable? A great idea? A terrible idea? Resources and any guidance appreciated.
Well, you're getting paid by the hour....
I don't see how involving the Greek alphabet is to anyone's advantage. If the queries are stored anywhere, everyone approaching the system would have to learn the new syntax to understand them. Plus, there's the problem of how to type the special symbols.
If the client creates complex regular expressions they'd like to be able to reuse, that's understandable. Your application could maintain a list of such expressions that the user could add to and choose from. Notionally, the user would "click on" an expression, and it would be inserted into the query.
The saved expressions could have user-defined names, to make them easier to remember and refer to. And you could define a syntax that referenced them, something otherwise invalid in SQL, such as ::name. Before submitting the query to the DBMS, you substitute the regex for the name.
You still have the problem of choosing good names, and training.
To prevent malformed SQL, I imagine you'll want to ensure the regex is valid. You wouldn't want your system to store a ; drop table CUSTOMERS; as a "regular expression"! You'll either have to validate the expression or, if you can, treat the regex as data in a parameterized query.
The real question to me, though, is why you're in the vicinity of standardized regex queries. That need suggests a database design issue: it suggests the column being queried is composed of composite data, and should be represented as multiple columns that can be queried directly, without using regular expressions.
I have a generated flatbuffers object in Java. I need to query for a field at runtime based on user input. Is there a way to do that?
There is currently no way to dynamically query fields in Java, you have to know the field's name statically to retrieve its value. So best you can do is if (user_input == "field") return obj.field().
There is a way to find out what fields are in a schema dynamically, by inspecting a binary schema file (which can be generated with flatc --schema myschema.fbs). Sadly, there is no reflection helper code in Java yet that will allow you to use that information to read an actual field (C++ only so far).
In most of the JSON schemas of hl7 FHIR resources, i found fields prefixed with _. But they are not listed in the examples. So while creating classes for the resources, shall I go only with fields not prefixed with _.
Like _assertedDate and assertedDate. Whether both fields are needed or not?
Because, for same resources in xml schema definition, I dont find _assertedDate.
you need to read the details about the json format at http://build.fhir.org/json.html (particularly http://build.fhir.org/json.html#primitive), and see http://build.fhir.org/observation-example-10minute-apgar-score.json for an example
I'm designing a RESTful API and I'm trying to work out how I could represent a predicate with OR an operator when querying for a resource.
For example if I had a resource Foo with a property Name, how would you search for all Foo resources with a name matching "Name1" OR "Name2"?
This is straight forward when it's an AND operator as I could do the following:
http://www.website.com/Foo?Name=Name1&Age=19
The other approach I've seen is to post the search in the body.
You will need to pick your own approach, but I can name few that seem to be pretty logical (although not without disadvantages):
Option 1.: Using | operator:
http://www.website.com/Foo?Name=Name1|Name2
Option 2.: Using modified query param to allow selection by one of the values from the set (list of possible comma-separated values):
http://www.website.com/Foo?Name_in=Name1,Name2
Option 3.: Using PHP-like notation to provide list instead of single string:
http://www.website.com/Foo?Name[]=Name1&Name[]=Name2
All of the above mentioned options have one huge advantage: they do not interfere with other query params.
But as I mentioned, pick your own approach and be consistent about it across your API.
Well one quick way to fixing that is to add an additional parameter that is identifying the relationship between your parameters wether they're an and or an or for example:
http://www.website.com/Foo?Name=Name1&Age=19&or=true
Or for much more complex queries just keep a single parameter and in it include your whole query by making up your own little query language and on the server side you would parse the whole string and extract the information and the statement.
I am looking for a tool that can serialize and/or transform SQL Result Sets into XML. Getting dumbed down XML generation from SQL result sets is simple and trivial, but that's not what I need.
The solution has to be database neutral, and accepts only regular SQL query results (no db xml support used). A particular challenge of this tool is to provide nested XML matching any schema from row based results. Intermediate steps are too slow and wasteful - this needs to happen in one single step; no RS->object->XML, preferably no RS->XML->XSLT->XML. It must support streaming due to large result sets, big XML.
Anything out there for this?
With SQL Server you really should consider using the FOR XML construct in the query.
If you're using .Net, just use a DataAdapter to fill a dataset. Once it's in a dataset, just use its .WriteXML() method. That breaks your DB->object->XML rule, but it's really how things are done. You might be able to work something out with a datareader, but I doubt it.
Not that I know of. I would just roll my own. It's not that hard to do, maybe something like this:
#!/usr/bin/env jruby
import java.sql.DriverManager
# TODO some magic to load the driver
conn = DriverManager.getConnection(ARGV[0], ARGV[1], ARGV[2])
res = conn.executeQuery ARGV[3]
puts "<result>"
meta = res.meta_data
while res.next
puts "<row>"
for n in 1..meta.column_count
column = meta.getColumnName n
puts "<#{column}>#{res.getString(n)}</#{column}"
end
puts "</row>"
end
puts "</result>"
Disclaimer: I just made all of that up, I'm not even bothering to pretend that it works. :-)
In .NET you can fill a dataset from any source and then it can write that out to disk for you as XML with or without the schema. I can't say what performance for large sets would be like. Simple :)
Another option, depending on how many schemas you need to output, and/or how dynamic this solution is supposed to be, would be to actually write the XML directly from the SQL statement, as in the following simple example...
SELECT
'<Record>' ||
'<name>' || name || '</name>' ||
'<address>' || address || '</address>' ||
'</Record>'
FROM
contacts
You would have to prepend and append the document element, but I think this example is easy enough to understand.
dbunit (www.dbunit.org) does go from sql to xml and vice versa; you might be able to modify it more for your needs.
Technically, converting a result set to an XML file is straight forward and doesn't need any tool unless you have a requirement to convert the data structure to fit specific export schema. In general the result set gets the top-level element of an XML file, then you produce a number of record elements containing attributes, which effectively are the fields of a record.
When it comes to Java, for example, you just need appropriate JDBC driver for interfacing with DBMS of your choice addressing the database independency requirement (usually provided by a DBMS vendor), and a few lines of code to read a result set and print out an XML string per record, per field. Not a difficult task for an average Java developer in my opinion.
Anyway, the more concrete purpose you state the more concrete answer you get.
In Java, you may just fill an object with the xml data (like an entity bean) and then use XMLEncoder to get it to xml. From there you may use XSLT for further conversion or XMLDecoder to bring it back to an object.
Greetz, GHad
PS: See http://ghads.wordpress.com/2008/09/16/java-to-xml-to-java/ for an example for the Object to XML part... From DB to Object multiple more way are possible: JDBC, Groovy DataSets or GORM. Apache Common Beans may help to fill up JavaBeans via Reflection-like methods.
I created a solution to this problem by using the equivalent of a mail merge using the resultset as the source, and a template through which it was merged to produce the desired XML.
The template was standard XML, with a Header element, a Footer element and a Body element. Using a CDATA block in the Body element allowed me to include a complete XML structure that acted as the template for each row. In order to include a fields from the resultset in the template, I used markers that looked like this <[FieldName]>. The template was then pre-parsed to isolate the markers such that in operation, the template requests each of the fields from the resultset as the Body is being produced.
The Header and Footer elements are output only once at the beginning and end of the output set. The body could be any XML or text structure desired. In your case, it sounds like you might have several templates, one for each of your desired schemas.
All of the above was encapsulated in a Template class, such that after loading the Template, I merely called merge() on the template passing the resultset in as a parameter.