I have a data table
and it contains some int type columns, some type double columns, some date type columns
what i am trying to do is,
i want to do double.TryParse for double column, and if there is any value with it then it will store dbnull value in corresponding rows,
same thing i will do for date, int
since my data table could have 100000 records so i don't to run loop for each row
is it possible through linq or with any method
Thank You
LINQ is not good for batch operations. You should create a stored procedure in your DB and import it in your model (If you are using EF that is import function, if using LINQ to SQL then a simple drag and drop will do it).
LINQ is no silver bullet for all problems where you need to loop over a (maybe very large) set of data. So if you want to go over each data set and change the values depending on some condition, a foreach loop is your friend.
LINQ is a query language to retrieve data and not some kind of super-fast way to alter large lists or other enumerable objects. It comes in handy if you want to get data from a given object applying some conditions or doing a GroupBy without ending up in a 20-lines unreadable mash of foreach-loops and if-statements.
It doesn't matter if you'll do it in a loop or with linq, you'll still need to iterate over the entire data table ...
there's no silver bullet that will save you from doing the checks and inserts i'm afraid
Related
I have a table which it has 2000 row. This tables "name" columns are static. But Others is dinamic. The table follow as :
Can i keep this table inside program? Which format must use? (Class,list, datatable, struct Json or etc.).
I'll search and update on table in future...
Thanks.
You can easily put your row data into a MyRow class with Id, Position, Weight and FullEmp properties and then put those row objects into a list of rows like List<MyRow>.
Performance considerations largely depend on what you want to do with your data. How often do you read it? How often do you change it? How often do you insert, append or remove rows? Which properties do you access during your search?
A list is a good starting point that you can use until you find out that the performance is unsatisfactory for your usecase.
I am wondering which method is the best way to store a list of integers in a sql column.
.....i.e. "1,2,3,4,6,7"
EDIT: These values represent other IDs in SQL tables. The row would look like
[1] [2]
id, listOfOtherIDs
The choices I have researched so far are:
A varchar of separated value that are "explode-able" i.e. by commas or tabs
An XML containing all the values individually
Using individual rows for each value.
Which method is the best method to use?
Thanks,
Ian
A single element of a record can only refer to one value; it's a basic database design principle.
You will have to change the database's design: use a single row for each value.
You might want to read up on normalization.
As is shown here in the description of the first normal form:
First normal form states that at every row and column intersection in the table there, exists a single value, and never a list of values. For example, you cannot have a field named Price in which you place more than one Price. If you think of each intersection of rows and columns as a cell, each cell can hold only one value.
While Jeroen's answer is valid for "multi-valued" attributes, there are genuine situations where multiple comma-separated values may actually be representing one large value. Things like path data (on a map), integer sequence, list of prime factors and many more could well be stored in a comma-separated varchar. I think it is better to explain what exactly are you storing and how do you need to retrieve and use that value.
EDIT:
Looking at your edit, if by IDs you mean PK of another table, then this sounds like a genuine M-N relation between this table and the one whose IDs you're storing. This stuff should really be stored in a separate gerund, which BTW is a table that would have the PK of each of these tables as FKs, thus linking the related rows of both tables. So Jeroen's answer very well suits your situation.
What is the best way to retrieve a "X" number of random records using Entity Framework (EF5 if it's relevant). The value of "X" will be set based on where this will be used.
Is there a method for doing this built into EF or is best to pull down a result set and then use a C# random number function to pull the records. Or is there a method that I'm not thinking of?
On the off chance that it's relevant I have a table that stores images that I use for different usages (there is a FK to an image type table). The images that I use in my carousel on the homepage is what I'm wanting to add some variety to...consequently how "random" it is doesn't matter to me much. I'm just trying to get away from the same six or so pictures always being displayed. (Also, I'm not really interested in debating/discussing storing images in a table vs local storage.)
The solution needs to be one using EF via a LINQ statement. If this isn't directly possibly I may end up doing something SIMILAR to what #cmd has recommended in the comments. This would most likely be a matter of retrieving a record count...testing the PK to make sure the resulting object wasn't null and building a LIST of the X number of object's PKs to pass to front end. The carousel lazy loads the images so I don't actually need the image when I'm building the list that will be used by the carousel.
Can you just add an ORDER BY RAND() clause to your query?
See this related question: MySQL: Alternatives to ORDER BY RAND()
I want to take a table as represented by a multidimensional string array (column names in another array) and use a SQL SELECT statement to get a subset of rows.
The Catch:
the table is input by the user (different table each time)
the SQL is also input by the user
Do I need to:
Create a table in SQL
Populate the table in SQL
Query the table
or is the a simpler solution? E.g. converting the multidimensional array to a DataTable and then running the SQL on that object?
I think you would be able to use DataTable for this. It's normally used to store data retrieved from a database but you can populate it manually. The best part is the DataTable.Select() method, which allows you to write just the WHERE clause of a query and it will return the matching rows.
You can create your own expression tree representing the query the user enters. This is how Linq works, under the hood. If you could give an example of what your trying to achieve it may help also what your going to write the application in c# for web for example.
For instance if you letting your users enter new rows, in some kind of GUI to a table then you could, do this in a datagrid and enable column filter to achieve the result mentioned above?
In a web app you could have an input box above each column users can enter data to filter that column on.
I have a table full of id's,categories and weights that I need to reference in my program as I read in records that contain those categories. What is the most efficient method to read those from a database and put into a structure that I can reference?
The ID's (and possibly the names) would be unique
Data might look like:
ID,Category,Weight
1,Assignment,5
2,Test,10
3,Quiz,5
4,Review,3
Your best bet is to read in your table using a DataReader, and put each row into an object containing Category and Weight, then each object into a Dictionary.
If you're using a later version of .NET, you could always use Linq to just grab that data for you.
If you want to avoid a database hit to fetch static data, you can hard-code the values into a common class in your solution. A Dictionary collection would work fine here too.
The trade off of course is; 2 locations to manage for any possible future changes.