I am building an app in which I have a Room entity that one of its columns is supposed to hold a List.
What is the best approach for doing this in an app that uses Flow, Coroutines and Room?
I tried serializing with Jackson (turning the List to a long json String and then bring it back to a List when fetched) but I am not sure if this is the correct approach.
Thank you,
What is the best approach for doing this in an app that uses Flow, Coroutines and Room?
This is very much open to opinion.
From a database perspective the approach would be to have any list as a table and thus
reducing the JSON bloat and thus reducing efficiency,
reduce duplication and thus be more likely to conform to normalisation
not potentially introducing complexities and even greater inefficiencies (e.g. not mentioned in the answer below but wild-character as the first character must do a full table scan)
perhaps consider this question and answer matching multiple title in single query using like keyword where if the table per list approach were taken then a simple SELECT * FROM task WHERE task_tags IN(:taglist) could do the same
From a coding point of view at first the coding is simpler when embedding JSON as the complex code is within the JSON libraries.
I have a conceptual/architectural question I'd like to get some input on. Before I go into the details, I'd like to mention that I am well-aware of the arguments against putting application logic into the database, and the importance of maintaining abstraction and separation of concerns.
That being said, the application in question is a fairly simple one, in which performance is relatively more important than best practices. It is a new app, built with very modern technologies but on old school principles (stored procs, no ORM, etc).
I have a fairly complex "summary view" which is going to be driven by data provided by a stored procedure. Most of the elements of this view are going to have permission logic (not trivial, but nothing too complex) which will change both the appearance as well as the nature of the data based on the permissions of the currently logged in user (i.e. some data could be anonymized, other could be hidden, etc).
All data, as well as membership and ACL records, are stored in the same database.
So, the question is where to put the logic of applying user rights. The two options are:
1) Bring back all relevant data from the database into domain objects, then apply permissions in the middle-tier
2) Pass a user ID to the stored proc, and have it pass back an already prepared result to the middle-tier
At first look, conceptually, the no-brainer seems to be to throw it into the middle-tier (1st option) and leave the database concerned with what it does best - reading and writing data. However, the stored procedure will already be "tailored" to the specific view (think something along the lines of a report), and not used for anything else; thus, it just seems easier and lighter to process the permissions inside of the stored proc and bring back a prepared result with all the permissions already applied (a result that would have less data), rather than bringing back ALL the data into the middle tier and processing permissions there (eventually to discard half of the data anyway).
I am a bit torn and would appreciate some input. Intuitively, the 2nd option seems like a better fit, but "feels" very wrong.
Design the stored procedure to accept privileges enabled or features to use, e.g.
PROCEDURE retrieve_data (id_or_other_params,
anonymize := FALSE,
hide := FALSE,
some_other_feature := FALSE);
Procedure concerns now data retrieval only, with modifying options read from external source. Now let middle tier authenticate the user, decide which options to use and pass them to the procedure.
I'm trying to understand choices for code generation tools/ORM tools and discover what solution will best meet the requirements that I have and the limitations present.
I'm creating a foundational solution to be used for new projects. It consists of ASP.NET MVC 3.0, layers for business logic and data access. The data access layer will need to go against Oracle for now, and then switch to SQL this year as the db migration is finished.
From a DTO standpoint mapping to custom types in the solution, what ORM/code generation tool will work with creating my needed code but can ONLY access Stored Procs in Oracle and SQL.?
Meaning, I need to generate the custom objects that are the artifacts from and being pushed to the stored procedures as the parameters, I don't need to generate the sprocs themselves, they already exist. I'm looking for the representation of what the sproc needs and gives back to be generated into DTOs. In some cases I can go against views and generate DTOs. I'm assuming most tools already do this. But for 90% of the time, I don't have access directly to any tables or views, only stored procs.
Does this make sense?
ORMs are best at mapping objects to tables (and/or views), not mapping objects to sprocs.
Very few tools can do automated code generation against whatever output a sproc may generate, depending on the complexity of the sproc. It's much more straight-forward to code generate the input to a sproc as that is generally well defined and clear.
I would say if you are stuck with sprocs, your options for using third party code to help reduce your development and maintenance time are severely limited.
I believe either LinqToSql or EntityFramework (or both?) are capable of some magic with regards to SQL Server to try to mostly automatically figure out what a sproc may be returning. I don't think it works all the time, it's just sophisticated guess work and I seriously doubt it would work with Oracle. I am not aware of anything else software-wise that even attempts to figure out what a sproc may return.
A sproc can return multiple diverse record sets that can be built dynamically by the sproc depending on the input and data in the database. A technical solution to automatically anticipating sproc output seems like it would require the following:
A static set of underlying data in the database
The ability to pass all possible inputs to the sproc and execute the sproc without any negative impact or side effects
That would give you a static set of possible outputs for any given valid input. A small change in the data in the database could invalidate everything.
If I recall correctly, the magic Microsoft did was something like calling the sproc passing NULL for all input parameters and assuming the output is always exactly the first recordset that comes back from the database. That is clearly an incomplete solution to the problem, but in simple cases it appears to be magic because it can work very well some of the time.
Is it possible to transform the returned data from a Find query in MongoDB?
As an example, I have a first and last field to store a user's first and last name. In certain queries, I wish to return the first name and last initial only (e.g. 'Joe Smith' returned as 'Joe S'). In MySQL a SUBSTRING() function could be used on the field in the SELECT statement.
Are there data transformations or string functions in Mongo like there are in SQL? If so can you please provide an example of usage. If not, is there a proposed method of transforming the data aside from looping through the returned object?
It is possible to do just about anything server-side with mongodb. The reason you will usually hear "no" is you sacrifice too much speed for it to make sense under ordinary circumstances. One of the main forces behind PyMongo, Mike Dirolf with 10gen, has a good blog post on using server-side javascript with pymongo here: http://dirolf.com/2010/04/05/stored-javascript-in-mongodb-and-pymongo.html. His example is for storing a javascript function to return the sum of two fields. But you could easily modify to return the first letter of your user name field. The gist would be something like:
db.system_js.first_letter = "function (x) { return x.charAt(0); }"
Understand first, though, that mongodb is made to be really good at retrieving your data, not really good at processing it. The recommendation (see for example 50 tips and tricks for mongodb developers from Kristina Chodorow by Oreilly) is to do what Andrew tersely alluded to doing above: make a first letter column and return that instead. Any processing can be more efficiently done in the application.
But if you feel that even querying for the fullname before returning fullname[0] from your 'view' is too much of a security risk, you don't need to do everything the fastest possible way. I'd avoided map-reduce in mongodb for awhile because of all the public concerns about speed. Then I ran my first map reduce and twiddled my thumbs for .1 seconds as it processed 80,000 10k documents. I realize in the scheme of things, that's tiny. But it illustrates that just because it's bad for a massive website to take a performance hit on some server side processing, doesn't mean it would matter to you. In my case, I imagine it would take me slightly longer to migrate to Hadoop than to just eat that .1 seconds every now and then. Good luck with your site
The question you should ask yourself is why you need that data. If you need it for display purposes, do that in your view code. If you need it for query purposes, then do as Andrew suggested, and store it as an extra field on the object. Mongo doesn't provide server-side transformations (usually, and where it does, you usually don't want to use them); the answer is usually to not treat your data as you would in a relational DB, but to use the more flexible nature of the data store to pre-bake your data into the formats that you're going to be using.
If you can provide more information on how this data should be used, then we might be able to answer a little more usefully.
In my travels in Oracle, the 'stragg' function, or 'String Aggregator' was life-saving when I had to create dynamic SQL queries on the fly.
You can read up about it here: http://www.oratechinfo.co.uk/delimited_lists_to_collections.html
The basic use of it was:
select stragg(fruit) from food;
fruit
-----------
apple,pear,banana,strawberry
1 row(s) returned
So simple to use, concatenating chr(13) turned it into a long list, and selecting information from system tables gave a 5 minute solution to dynamically generated SQL, e.g. auditing triggers.
Now I've been charged with transferring oracle functionality related to auditing into Sybase, and a function similar to Stragg would be ideal for this purpose.
E.g.
select #my_table = 'table_of_fruit'
select 'insert into '+#mytable+'_copy (' +char(10)
+ stragg(c.name) +char(10)
+ 'select '
+ stragg('inserted.'+c.name) + char(10)
+ 'from '+#mytable
from syscolumns c
where objectid(#mytable) = c.id
------------------------------------------
insert into table_of_fruit_copy
(fruit, sweetness, price)
select fruit, sweetness,price
from inserted
Done. Simple.
Except I don't know how to get a string-aggregation function working in Sybase.
Does anyone know of an attempt to do this kind of thing, or code that could work the same as stragg that could be used in this way?
The alternative at the moment is printing code based on complex cursors and such (sample LOC: 500), or select statements combining static strings and columns from user tables (sample LOC: 200). Stragg would severely reduce the complexity of this code, and would be a great deal of help in the future (sample LOC: who knows, maybe 50?)
p.s. I'm calling these selects through a shell script then piping them to file, then running the file through iSQL. Not the nicest solution, but it's better than the alternatives.
There are three separate answers
Question
You have made comments about simplicity, which need to be addressed before we get to the solution.
It is a common requirement to be able to take a delimited list of values, say A,B,C,D, and treat this data like it was a set of rows in a table, or vice versa
This one of the Top Ten Worst Programming Practices I read about recently.
In general, Sybase types tend to be somewhat more academically and Relationally qualified than Oracle types, so we simply do not do that sort of thing in SybaseLand or DB2Land.
In 20 years of working with Sybase, I have had to code that as part of my project just once, and that was for non-technical Auditor who loaded the result set into MS Access.
On the other hand, I have had to code that at least 12 times, when producing text files for importation into Oracle databases (fulfilling external requirements is outside my project, but I satisfy any such requirement free). Obviously the target databases were sub-standard and non-relational (loading a column with more than one datum breaks 1NF, and creates Update Anomalies), which is typical of what Oracle types have to do to get some speed.
Therefore, no, it is not simplicity, at least in the sense of that principle. It is by definition, complexity.
Your reference to "arrays" is incorrect. All commercial dbms handle arrays, according to the ISO/IEC/ANSI SQL (STRAGGR and LIST operators are non-standard SQL, therefore not SQL). Sybase is very strong in processing arrays. If it was an array, you would not need special hand coding to handle it (and you do, as per your question). This is not an array, there is no definition to the cells. This is a single concatenated scalar string.
Pivoting is an entirely different process, which uses set-processing; it does not require row-processing. (I understand on good authority, that Oracle is hopeless at scalar subqueries, and thus Oracle people are used to writing them as [very inefficient] joins or inline views, and then filtering: all that can be elevated to set-processing via scalar subqueries, and it will perform much faster. Particularly your Pivots.)
Even the author in your link posts as follows. Please familiarise yourself with the caveats:
It's as simple as this: If you want to have a system with no logical limitation in the number of data elements passed to a given process, then forget the following mechanisms! They are simply the wrong way to approach the problem.
Therefore, know whatever you are doing is sub-standard, non-relational, and limited; and go ahead with your eyes open. No use pretending that: it will not break; it is not limited; it is an "array"; or that Sybase doesn't have a neat little function that Oracle has. Any professional will see through all that. And if the string length is exceeded, for God's sake send some indicator back to the caller ("!Exceeded" in the string) identifying that condition.
Essentially you are turning the set-processing engine on its head, and forcing it into row-processing mode, so it will be very slow. A WHILE loop is distinctly faster than a cursor, but both are in the same class, row-processors.
The alternative at the moment is printing code based on complex cursors and such
What 200 or 500 LoC ? It is possible I am missing something, but my code is the same few lines of code identified under "Using a Table Function" in your link. Maximum 20, if you count nice formatting; the loop; initialisation; error handling. There is nothing "complex" about it. Do the exact reverse to cancatenate a single string from multiple rows. We use stored procedures for this (which oracle does not have, really, PL/SQL is a different animal). If you have ASE 15.0.2 or greater, you can use a User Defined Function, which you can then use in place of a column. Stored procs are better for true arrays.
the concatenation operator in Sybase is the plus sign. For reversal (decomposing the CSV string) you need CHARINDEX and SUBSTRING functions
You may need the Function Reference Manual, if for nothing else, to avoid writing code where we have functions.
Likewise, we do not have a RANK() function. We are quite happy with the 4 lines of code requires for the subquery. It is only required for Oracle because subqueries are crippled.
Ok, I have answered your question, Now to address the approaches.
You will be aware that code using Oracle Extensions to the SQL standard will need to be changed.
Sybase is way more automated than Oracle; if you familiarise yourself with its feature set, in many instances, you can get the same result (as you did in Oracle) without writing any code. Writing code-for-code blocks is the chain gang, rock-breaking method of building roads, in the context of bulldozers. Even if your company had good reason to use that method, you need to the aware that features work quite differently, eg. triggers, which is why I am posting so much detail.
Another issue that will annoy you is that Oracle isn't really ANSI SQL compliant (stretches the definitions in many places, in order to appear to be compliant), and Sybase, given its customer base, is rigidly SQL compliant. So in addition to the same function working differently, or in a different deployment, you need to be aware that code changes may be required to elevate Oracle code to ANSI compliance levels, just to execute on an ANSI SQL compliant platform.
I am not sure if you are trying to write code for the content of a trigger, or if you are trying to capture the changes to a database. I will provide both answers.
Auditing
Capture Changes to Database
We have an very robust, fast and configurable Auditing subsystem, fit for high volumes and banking level auditing requirements. Get your DBA to setup the sybaudit (separate) database, and to configure exactly what changes need to be captured. This facility will perform much faster than any code you or I can write in a trigger (as much as 100 times faster than your row-by-processing required for the above, as it is executed within the engine, within your executing thread). And of course the setup time is a fraction of your coding time.
Triggers
Again, I am not sure exactly what you are trying to achieve, but assuming you want to copy every insert to some table to a COPY of that table (inside the Trigger), that example code you have provided will not work (and I am not counting syntax issues).
Speaking to your example, you need to do way more work, to deal with the different datatypes; column sizes; precisions; scale; etc. And perhaps the UPDATE() function to identify which columns have changed (for an UPDATE trigger of course). If all you are trying to do is convert the various datatypes to strings, check the CONVERT() function.
Triggers are transactional.
Never place row-processing code in a Trigger (it will strangle the table)
You can't place Dynamic SQL in a Trigger.
But in Sybase even that is not necessary. Refer to the User Guide, chapter 19 is devoted to Triggers, with several variations, and examples. Inside the trigger, you should be able to simply:
INSERT table_copy
SELECT column_list -- never use * unless you want the db fixed in cement
FROM inserted
If you are trying to copy the inserts to all tables into one Audit table, then beware. Then I understand your example a little bit more. You will be forcing a highly Symmetric Muli-Threading server (oracle is not a server in the architecture sense) into single-threading through your table. Auditing is multi-threaded.
Last, the use of manual methods of any kind is not required, so if you could expand a bit more on your PS, what the requirement you are trying to fulfil is, I can identify the programmatic method for you. It appears you are trying to use the PL/SQL approach (which is very limited).
Just use the LIST() function. It's a direct replacement for stragg() function. Example:
SELECT LIST(state, ', ') FROM cities
Result:
name
CA, CA, MA, NY