I have a MySQL database with column 'apps_owned'. Everytime a user buys an app, I want their row to have the AppID added to it. For example,
apps_owned = 1, 4, 75 etc.
How would I do this?
Next, I need to split these up into individual numbers in C#. I don't know how I would remove the comma's to get a whole number. Is there any way of doing this. I know how to get the numbers from the database, I just don't know how to add to them or split them. Is there any easier way to do this?
Let the DB do the work, have a table represent a users apps. Then you could simply count, add, delete...
To Split you can do something like:
var result = apps_owned.Split(' ').Select(x => int.Parse(x.ToString.Replace(",", ""))).ToArray<int>();
Related
Hi I am using Visual Studio 2013, c# asp.net. I have created a online docket for staff to fill out, I was wondering can you add a reference number/ issue number to the web form. Each staff member will fill out this form and they could be similar, so I want each form to have there own unique number however I am not to sure which way to go about it. The form is going to be the same for everyone so I want each one that is filled out to have a different number. Should I place a label and have an array list to generate random numbers or is there a more straight forward way?
An alternative to keeping a number in the database and having to detect collisions etc you could use the Guid: Guid.NewGuid()
Sample usage:
Guid uniqueId = System.Guid.NewGuid();
string x = uniqueId.ToString();
Keep a number in a database. On each form generated, take this number, increment it, and save the new number to the DB.
I have a mysql database. In which there are 50 columns of detail.
Detail 1, Detail2, Detail3...... Detail50.
I have the website locally so i am scrapping from myself. The site is not in order no tags and names data is just in form of text line by line, so this was the only option to take what i get line by line and save to DB. So every line gets a column from 1-50....
Some pages have 10 columns other have 50 and the data is in no order now i have the DB,how can i sort them any suggestion ,idea is welcome.
This image will make it more clear:
So You can see Sometimes its Inner Diameter in Detail4 and sometime in 1, these are just examples i would have hard coded but there are too many possibilities, but the repeating words all have the same staring name just values different .Any chance to atleast make 50 % of the data in order the ones with same 4-5 starting words like
part,inner,diameter,oil filter etc.
Any suggestion or ideas can it be done in mysql or C# code.....
Thank you
your approach is totally wrong, but if you want to go this way, just make a table with two columns 'id' and 'details' ... make an insert for each column for the specific product ID.
After that you can use a SELECT like that:
select SUBSTRING(details, 14) from products where details like 'Inner Diameter%' and id = 'my_product_id';
I have a page with 26 sections - one for each letter of the alphabet. I'm retrieving a list of manufacturers from the database, and for each one, creating a link - using a different field in the Database. So currently, I leave the connection open, then do a new SELECT by each letter, WHERE the Name LIKE that letter. It's very slow, though.
What's a better way to do this?
TIA
Since you are going to fetch them all anyway, you might find it faster to fetch them in one go and split them into letter-groups in the code.
Looking at it from the other end, why do you need to fetch all the lists just to build a set of links? Shouldn't you fetch a single letter when its link is clicked?
It sounds like you are doing up to 26 queries, which will never be fast. Often a single db query can take at least 40 ms, due to network latency, establishing connection, etc. So, doing this 26 times means that it will take around 40 x 26 ms, or more than one second. Of course, it can take much longer depending on your schema, data set, hardware, etc., but this is a rule of thumb that gives you a rough idea of the impact of queries on overall page render time.
One way I deal with this kind of situation is to use a DataTable. Fetch all the records into the DataTable, and then you can iterate through the alphabet, and use the Select method to filter.
DataTable myData = GetMyData();
foreach(string letter in lettersOfTheAlphabet)
{
myData.Filter(String.Format("Name like '{0}%'", letter));
//create your link here
}
Depending on your model layer you may wish to filter in a different way, but this is the basic idea that should improve the performance a lot.
Assuming you are querying to determine which letters are used, so that you know which links to render, you could actually just query for the letters themselves, like this:
select distinct substring(ManufacturerName, 1, 1) as FirstCharacter
from MyTable
order by 1
get one result set from one query and split that up. There is quite a lot of overhead going out the the database 26 times to do basically the same work!
You could probably do it smarter with a stored procedure. Let the SP return all the information you need in one call, and suddenly you only have one database interaction instead of 26...
Bring back all the items in one set (dataset, etc..), either through stored procedure or query, including the field left(col1,1), and sorting by that field..
select left(col1,1) as LetterGroup, col1, url_column from table1 order by left(col1,1)
Then look through the whole resultset, changing sections when the letter changes.
First letter in the alphabet sucks (sorry) as discriminator. You do not neet to split them actually (you could just ask for "where name like 'a%'), but whatever you run for that gives you on average a 1/26 or so split of the names. Not extremely efficient.
What do you mean with "creating a link - using a different field in the Database" - this sounds like a bad design to me.
there are a couple ways u can do this. 1) create a view in your db that has all the manufactures and their website link and then continue to hit the view for each letter. 2) select all the manufactures once and store it in a .net dataset and then use that dataset to populate your links.
This seems dirty to me, but you could create a first letter CHAR column and trigger to populate it. Have the first letter from the manufacturer name stored in that column and index it. Then select * from table where FirstLetter = 'A'.
Or create a lookup table with rows A - Z and set up foreign key in the manufacturer table. Again you would probably need a trigger to update this information. Then you could inner join the lookup table to the manufacturer table.
Then instead of putting 26 datasets in the page, have a list of links (A-Z) which select and show each dataset one at a time.
If I read you right, you're making a query for every manufacturer to get the "different field" you need to construct the link. If so, that's your problem, not the 26 alphabetic queries (though that's no help).
In a case like that, the faster way is this one query:
SELECT manufacturer_name, manufacturer_id, different_field
FROM manufacturers m
INNER JOIN different_field_table d
ON m.manufacturer_id = d.manufacturer_id
ORDER BY manufacturer_name
In your server code, loop through the records as usual. If you want, emit a heading when the first letter of the manufacturer_name changes.
For additional speed:
Put that in a stored procedure.
Index different_field_table on manufacturer_id.
I have a calendar that I generate. Currently it makes the entire month and fills each cell with a number(representing the date).
Now I want to grab values from a database and fill in the cells. How could I do this efficiently?
Like right now I can only think of grabbing the data from the database. Once that is down going through that data and essentially have like 30 if statements to determine what cell it should go into.
So that just seems like a very bad way and I am thinking of better ways. So I am wondering anyone else has any ideas.
I am using asp.net mvc I generate the body of the calendar(what is just a table) through my controller and pass it as just a string of html cells and rows.
So basically I generate in the controller all 6 rows of 7 cells(42 cells with 2 cells for previous month and remaining cells for the next month - basically looks like the windows 7 calendar) with the TagBuilder and return that as one big string.
So while building the cells that's what I would have to put the if statements to do the checking.
I am using linq to sql by the way so not sure if that will help or not.
Edit
Another way what I was thinking but not sure how to do it. Would be some how getting all the dates in range. Then take those results and do some grouping on those results. Not sure how to that kind of grouping though. It probably would not be to bad if I do the grouping on the first results and not do a request for each date and then group that. Otherwise I am looking at like 42 requests to the database to group everything.
You're having to loop anyway, to build the rows and columns I assume, so why not pull the data down first, for that month, put the data into an array (old fashioned I know), and check the offset in that array as you increment through the cell rendering?
I was wondering if anyone has a good solution to a problem I've encountered numerous times during the last years.
I have a shopping cart and my customer explicitly requests that it's order is significant. So I need to persist the order to the DB.
The obvious way would be to simply insert some OrderField where I would assign the number 0 to N and sort it that way.
But doing so would make reordering harder and I somehow feel that this solution is kinda fragile and will come back at me some day.
(I use C# 3,5 with NHibernate and SQL Server 2005)
Thank you
Ok here is my solution to make programming this easier for anyone that happens along to this thread. the trick is being able to update all the order indexes above or below an insert / deletion in one update.
Using a numeric (integer) column in your table, supported by the SQL queries
CREATE TABLE myitems (Myitem TEXT, id INTEGER PRIMARY KEY, orderindex NUMERIC);
To delete the item at orderindex 6:
DELETE FROM myitems WHERE orderindex=6;
UPDATE myitems SET orderindex = (orderindex - 1) WHERE orderindex > 6;
To swap two items (4 and 7):
UPDATE myitems SET orderindex = 0 WHERE orderindex = 4;
UPDATE myitems SET orderindex = 4 WHERE orderindex = 7;
UPDATE myitems SET orderindex = 7 WHERE orderindex = 0;
i.e. 0 is not used, so use a it as a dummy to avoid having an ambiguous item.
To insert at 3:
UPDATE myitems SET orderindex = (orderindex + 1) WHERE orderindex > 2;
INSERT INTO myitems (Myitem,orderindex) values ("MytxtitemHere",3)
Best solution is a Doubly Linked list. O(1) for all operations except indexing. Nothing can index SQL quickly though except a where clause on the item you want.
0,10,20 types fail. Sequence column ones fail. Float sequence column fails at group moves.
Doubly Linked list is same operations for addition, removal, group deletion, group addition, group move. Single linked list works ok too. Double linked is better with SQL in my opinion though. Single linked list requires you to have the entire list.
FWIW, I think the way you suggest (i.e. committing the order to the database) is not a bad solution to your problem. I also think it's probably the safest/most reliable way.
How about using a linked list implementation? Having one column the will hold the value (order number) of the next item. I think it's by far the easiest to use when doing insertion of orders in between. No need to renumber.
Unfortunately there is no magic bullet for this. You cannot guarentee the order of any SELECT statement WITHOUT an order by clause. You need to add the column and program around it.
I don't know that I'd recommend adding gaps in the order sequence, depending on the size of your lists and the hits on the site, you might gain very little for the over head of handling the logic (you'd still need to cater for the occasion where all the gaps have been used up). I'd take a close look to see what benifits this would give you in your situation.
Sorry I can't offer anything better, Hope this helped.
I wouldn't recommend the A, AA, B, BA, BB approach at all. There's a lot of extra processing involved to determine hierarchy and inserting entries in between is not fun at all.
Just add an OrderField, integer. Don't use gaps, because then you have to either work with a non-standard 'step' on your next middle insert, or you will have to resynchronize your list first, then add a new entry.
Having 0...N is easy to reorder, and if you can use Array methods or List methods outside of SQL to re-order the collection as a whole, then update each entry, or you can figure out where you are inserting into, and +1 or -1 each entry after or before it accordingly.
Once you have a little library written for it, it'll be a piece of cake.
I would just insert an order field. Its the simplest way. If the customer can reorder the fields or you need to insert in the middle then just rewrite the order fields for all items in that batch.
If down the line you find this limiting due to poor performance on inserts and updates then it is possible to use a varchar field rather than an integer. This allows for quite a high level of precision when inserting. eg to insert between items 'A' and 'B' you can insert an item ordered as 'AA'. This is almost certainly overkill for a shopping cart though.
On a level of abstraction above the cart Items let's say CartOrder (that has 1-n with CartItem) you can maintain a field called itemOrder which could be just a comma - separated list of id(PK) of cartItem records relevant . It will be at application layer that you require to parse that and arrange your item models accordingly . The big plus for this approach will be in case of order reshufflings , there might not be changes on individual objects but since order is persisted as an index field inside the order item table rows you will have to issue an update command for each one of the rows updating their index field.
Please let me know your criticisms on this approach, i am curious to know in which ways this might fail.
I solved it pragmatically like this:
The order is defined in the UI.
The backend gets a POST request that contains the IDs and the corresponding Position of every item in the list.
I start a transaction and update the position for every ID.
Done.
So ordering is expensive but reading the ordered list is super cheap.
I would recommend keeping gaps in the order number, so instead of 1,2,3 etc, use 10,20,30... If you need to just insert one more item, you could put it at 15, rather than reordering everything at that point.
Well, I would say the short answer is:
Create a primary key of autoidentity in the cartcontents table, then insert rows in the correct top-down order. Then by selecting from the table with order by the primary key autoidentity column would give you the same list. By doing this you have to delete all items and reinsert then in case of alterations to the cart contents. (But that is still quite a clean way of doing it) If that's not feasible, then go with the order column like suggested by others.
When I use Hibernate, and need to save the order of a #OneToMany, I use a Map and not a List.
#OneToMany(fetch = FetchType.EAGER, mappedBy = "rule", cascade = CascadeType.ALL)
#MapKey(name = "position")
#OrderBy("position")
private Map<Integer, RuleAction> actions = LazyMap.decorate(new LinkedHashMap<>(), FactoryUtils.instantiateFactory(RuleAction.class, new Class[] { Rule.class }, new Object[] { this }));
In this Java example, position is an Integer property of RuleAction so the order is persisted that way. I guess in C# this would look rather similar.