I'm going to generate some invite code. I know a simple method: do n-times loop to get a n-length random string. But it seems that when i want to check the code, it will cost more to find if a code is in data table using a string.
So, what is the best practice to create invite code?
(Old question, but pertinent to some code I'm writing just now...)
Use a GUID, and put an index on the column in the table. No problem with that.
Related
I currently try to solve the following issue in Tableau:
In the end, I would like to have a Tableau dashboard where the user can select a Customer, and then can see the Customer's KPIs. Nothing spectacular so far.
To obtain a Customer's KPIs, there is a CustomSQL query with a parameter "CustomerName" (that returns the KPIs for that Customer).
Now the thing:
I don't want to have a hardcoded list of CustomerNames, as it would be possible with Tableau Parameters. Instead, the CustomerNames should be fetched from another datasource. I did not find a way to "link" a Parameter to a DataSource, and/or inject something other than static Parameters into CustomSQL.
My Question: Is there really no solution for this, or am I just doing something wrong (I hope so).
I found this workaround here https://www.interworks.com/de/blog/daustin/2015/12/17/dynamic-parameters-tableau that seems to work, but that looks like... a workaround.
Few background info:
I have to stick to using a CustomSQL because
It is not viable for me to calculate all KPIs for all CustomerNames
and then filter by Tableau, since the data amount is too big.
It is not viable to replace the CustomSQL with Tableau Calculations
and Filters (already tried that, ended up in having Tableau pulling
too much data instead of pushing the work to the database).
I cannot believe that Tableau does not offer a solution here, since the use case is pretty common I believe.
Do you have some input for me?
Thank you for your help in advance!
Kind Regards
have you tried using rawsql() functions together with stored functions on the database side? I found it pretty useful when needed to load single value from the dataset completely not related to currently used datasource.
For example, running foo stored function which accepts 2 dates and calculated sum of something, Syntax should be something like:
rawsql_int(your_db_schema.foo(%1,%2),[startDateFieldTableau],[endDateFieldTableau])
but you can access it directly:
rawsql_int("select sum(bar) from sales")
but this is bit risky.
Drawbacks:
it relies on the current connection (you create a calculated field (duh!)
it will not work with extract (but you are using custom sql anyways so I believe you are more into live connection
I am working on an app where users can create posts that uses Amazon DynamoDB. One of the attributes of a post item in the database is postId. I am searching for the best practice to set this value upon creation. So far, I have thought of:
Counting the current items in the DB and then assigning the value as postId = dbcount + 1. I cannot find a count method for DynamoDB using Swift, and the ways I have found (scan & description) are either inefficient or accurate. Also, I thought of the scenario of 2 users posting at the same time.
I could create a UUID with Swift and set the postId to this value.
Upon these 2 options, which route is better? Is there a preferred industry standard? Option 2 seems to be the better choice, but I am not sure. Are there any other potential alternatives? Thank you!
I would definitely stay away from option 1 - as you said the potential for a race condition is too high and it could be expensive to implement too.
A UUID would certain work and is likely to be the least painful. However, there are other options too. An atomic counter would work. A bit more complicated but you could even use a conditional write. But the logic for that would be a pain.
The advantage of the UUID is that you generate it so that it can be used for, as an example, a row of data in a child table.
This question is about why I would use the above keywords. I've found plenty of MSDN pages that explain how. I'm looking for the why.
What query would I be trying to write that means I need them? I ask because the examples I have found appear to be achievable in other ways...
To try and figure it out myself, I created a very simple entity model using the Employee and EmployeePayHistory tables from the AdventureWorks database.
One example I saw online demonstrated something similar to the following Entity SQL:
SELECT VALUE
DEREF(CREATEREF(AdventureWorksEntities3.Employee, row(h.EmployeeID))).HireDate
FROM
AdventureWorksEntities3.EmployeePayHistory as h
This seems to pull back the HireDate without having to specify a join?
Why is this better than the SQL below (that appears to do exactly the same thing)?
SELECT VALUE
h.Employee.HireDate
FROM
AdventureWorksEntities3.EmployeePayHistory as h
Looking at the above two statements, I can't work out what extra the CREATEREF, DEREF bit is adding since I appear to be able to get at what I want without them.
I'm assuming I have just not found the scenarios that demostrate the purpose. I'm assuming there are scenarios where using these keywords is either simpler or is the only way to accomplish the required result.
What I can't find is the scenarios....
Can anyone fill in the gap? I don't need entire sets of SQL. I just need a starting point to play with i.e. a brief description of a scenario or two... I can expand on that myself.
Look at this post
One of the benefits of references is that it can be thought as a ‘lightweight’ entity in which we don’t need to spend resources in creating and maintaining the full entity state/values until it is really necessary. Once you have a ref to an entity, you can dereference it by using DEREF expression or by just invoking a property of the entity
TL;DR - REF/DEREF are similar to C++ pointers. It they are references to persisted entities (not entities which have not be saved to a data source).
Why would you use such a thing?: A reference to an entity uses less memory than having the DEFEF'ed (or expanded; or filled; or instantiated) entity. This may come in handy if you have a bunch of records that have image information and image data (4GB Files stored in the database). If you didn't use a REF, and you pulled back 10 of these entities just to get the image meta-data, then you'd quickly fill up your memory.
I know, I know. It'd be easier just to pull back the metadata in your query, but then you lose the point of what REF is good for :-D
I am trying to solve a homework problem where I have to return a selected users' grades in
order by course number (not allowed to use built-in sort function). I don't understand the results: the first entry isn't sorted, and some extra students seem to be returned. I don't know why and I spent over three hours trying to solve this one problem. Thanks.
A good start would be to get rid of functions like car, cdr, cadar, ...
Write access functions for the data records. Use first, second and third.
For accessing the list's first element use the function FIRST.
For accessing the rest of the elements use the function REST.
This makes the code easier to read and understand.
I like knockoutjs, the sooner we get rid of coding directly toward the DOM the better. I'm having trouble understanding how I would do something which I'm going to explain in terms of a question/answer site. (This is probably a general MVC/MVVM question)
In my data model I have a question[id, description] and answer[id, question_id, text]. The browser requests a list of questions which is bound to a tbody, one column will display the question description, while the other should be bound to an answer textbox.
One obvious way of doing this is to have a QuestionAnswer[question_id, answer_id, question_descrition, answer_text] model. Ideally I'd like to keep them separate to minimize transformation when sending/receiving/storing, if there isn't some way of keeping them separate then I have the following question:
Where is the ideal place to create the QuestionAnswer model ? My bet is that by convention its created on the server.
If there is such an example somewhere please point me to it, otherwise I think it would make a good example.
Please help me wrap my head around this, Thanks!
What you could do is to create the combined model on the server, serialize it to json and then use the mapping plugin to add the serialized list to the view model.
I'm doing that here only it isn't a combined model, but shouldn't make any difference. Especially since it seems like your relation is one-to-one.
If you need to create an "object" in your view model, you can use the mapping definition to do so, like I do here.
I use C# to build my model on the server, but I guess you can use whatever you are comfortable with.
The cool thing with the mapping plugin is that it adds the data to the view model so that you can focus on behaviour.
Ok,
I'v gathered my thoughts on what my question is actually asking.
To do data binding on the client side you obviously need your data model there as well. I was conflicted on what I needed to send over and at what time.
To continue with the Question/Answer site idea: Sending down a list of answers each of which have a question in them is what should be done. That way you can bind to the answer list and simply bind the question description of each answer to the first table column.
If later I want to make a question editor I would potentially send a complete different data structure down and not reuse the Answer has a Question structure previously used.
I thought there might be a way of sending down a more complex data structure that references itself. Which apparently is possible in JSon with some extra libraries.