Most of the examples I've found deal with Linq to entities, which is not what I need. I have a standard DataTable which I need to modify before returning to the caller. I can iterate over the normal Table.Rows collection or do something like this with the new extension methods:
foreach (var x in table.AsEnumerable()) {
if (x.Field<int>("SomeField") > SomeValue)
x.SetField<string>("OtherField", "OtherValue");
}
But I'm still manually looping through the entire row collection. Not necessarily a big deal, but I'm wondering if there's a more elegant way to accomplish this with Linq somehow, in the sense that I need to create an expression that iterates over the results of a query and performs an arbitrary action, rather than just select elements from the container being enumerated.
I think what you're wondering is if there's some sort of extension method like
stuff.ForEach(x => x.Value = "new value");
Unfortunately, there is no such thing. When I began using LINQ to SQL, I wanted the same thing. But unfortunately, you must use a for loop.
Related
I am trying to do string replace on entries of a column inside a db table. So far, I have reached till here:
$misa = DB::table('mis')->pluck('name');
for($i=0;;$i++)
{
$misa[$i] = substr_replace("$misa[$i]","",-3);
}
The error I am getting is "Undefined offset:443".
P.S. I am not a full-fledged programmer. Only trying to develop a few simple programs for my business. Thank You.
Since it's a collection, use the transform() collection method transform it and avoid this kind of errors. Also, you can just use str_before() method to transform each string:
$misa = DB::table('mis')->pluck('name');
$misa->transform(function($i) {
return str_before($i, ':ut');
});
There are a few ways to make this query prettier and FASTER! The beauty of Laravel is that we have the use of both Eloquent for pretty queries and then Collections to manage the data in a user friendly way. So, first lets clean up the query. You can instead use a DB::Raw select and do all of the string replacing in the query itself like so:
$misa = DB::table('mis')->select(DB::raw("REPLACE(name, ':ut' , '') as name"));
Now, we have a collection containing only the name column, and you've removed ':ut' in your specific case and simply replaced it with an empty string all within the MySQL query itself.
Surprise! That's it. No further php manipulation is required making this process much faster (will be noticeable in large data sets - trust me).
Cheers!
I have an EntityCollection ec in C# which has been populated with all Accounts.
Now I want another List or EntityCollection from ec which has all the accounts with status active.
I am using Linq for the same.
But both form of LINQ returns a an empty result while ec has 354 number of records
var activeCRMEC = (from cl in ec.Entities
where cl.Attributes["statecode"].ToString()=="0"
select cl);
OR
var activeCRMEC = ec.Entities.Where(x => x.Attributes["statecode"].ToString() == "0");
Each time the resultset is empty and I am unable to iterate over it. And 300 or so accounts are active, I have checked.
Same thing happens when I use some other attribute such as name etc.
Please be kind enough to point out my mistake.
You can Generate Early Bound Classes to write Linq Queries.
or Else
You can Write Linq Queries Using Late Bound Using OrganizationServiceContext Class.
For Your Reference:
OrganizationServiceContext OrgServiceCOntext = new OrganizationServiceContext(service);
var RetrieveAll = OrgServiceCOntext.CreateQuery("account").
ToList().Where(w => (w.GetAttributeValue<OptionSetValue>("statecode").Value ==0)).Select(s=>s);
I'll give you a few hints, and then tell you what I'm guessing your issue is.
First, use early bound entities. If you've never generated them before, use the earlybound generator, you'll save yourself a lot headaches.
Second, if you can't use early bound entities, use the GetAttribute() method on the Entity class. It'll convert types for you, and handle null reference issues.
Your LINQ expressions look to be correct, so either the ec.Entities doesn't have any entities in it that match the criteria of "statecode" equaling 0, or you possibly have some differed execution occurring on your IEnumerables. Try calling ToList() on the activeCRMEC immediately after the LINQ statement to ensure that is not your issue.
The statecode is an OptionSetValue, you should cast it in this way
((OptionSetValue)cl.Attributes["statecode"]).Value == 0
or
cl.GetAttributeValue<OptionSetValue>("statecode").Value == 0
Both ways are valid and you should ask for the Value that it is an int.
Hope this can help you.
I'm brand new to .NET 4.5, bootstrap, and LINQ and I've come across an issue I don't know how to handle elegantly. I was hoping somebody could confirm or correct my thought process, and if you're feeling particularly charitable, point me to a resource that could help me achieve my aim.
I'm developing a page on a web app that is going to link to multiple outside applications. The way I've decided to group the apps is by using a bootstrap Tab control, and making each tab a logical group. I've written the LINQ query that returns all of the information about the apps I need (Title, Description, Link, etc.), but now I need to group the results by another field (which we call ContainerID) and put the groups in their proper Repeater control inside the correct Bootstrap tab.
As of now I'm putting one Repeater inside of each tab, which feels a little clunky, but I can't think of a better way to do it. My idea was to do the following:
1) do a foreach loop on the objects returned by the LINQ query
2) inside the foreach loop, write an if statement like "if ContainerID=" then add the result to a list or array and use that as the datasource for the corresponding Repeater and bind it
3) rinse and repeat for however many categories I need.
As I started down this path it looks to me like there's no such thing as a foreach with LINQ, so I'm dead at step 1. Any thoughts on the best way to accomplish my aim? Thanks in advance...
EDIT: I should mention I'm not tied to any of this. If there's a better UI design to accomplish my purpose, I'm all for it. I'm just looking for the cleanest way to implement it.
The results of a linq query is just the query itself. There are no results until you iterate over the result. You should then be able to iterate over the results like this:
var items = Your LINQ Query
foreach(var item in items)
{
if(ContainerID == item.id)
{
//do work
}
}
Or you can do a items.ToList() which will iterate the query and turn it into a list of objects that you can work with. Hope this helps.
The following LINQ query works fine except when there are no results to return. Then an InvalidOperationException is thrown.
What is the best way to handle this? How do I test for the existance of a result and move along if there is none? I thought about a try-catch but felt there must be a more elegant solution.
In this example, I'm only expecting the Id of the first result. There may be other case where I want the entire object returned.
var drId = dcDest.drs.Where(dr => dr.ContactID == contactId)
.Select(dr => dr.Id).First();
int xId = drId;
You should use SingleOrDefault().
FirstOrDefault() could work too but really you are saying that there should only be one in the collection which makes 'SingleOrDefault()' the more proper choice (it will throw an exception if there is more than one).
If on the other hand you are expecting a sequence but need to handle the case when no elements are returned you can also use DefaultIfEmpty() to return a default value when the sequence is empty. See http://msdn.microsoft.com/en-us/library/bb355419.aspx
What behavior do you want when it is empty? An id of Zero or something else?
I have a course table which I need to search based on keywords typed in the search box.
Here is a sample query:
SELECT * FROM Courses WHERE
Title LIKE '%word%' OR Title LIKE '%excel%' OR
Contents LIKE '%word%' OR Contents LIKE '%excel%'
How can I convert this in LINQ where LINQ would dynamically generate WHERE statements based on each keywords.
I tried to user PredicateBuilder it works fine as long as the field is VARCHAR. For the "TEXT" fields the quotes are not generated thus causing compiler to give an error message. Here is the SQL generated by PredicateBuilder
SELECT [t0].[CoursesID], [t0].[Title], [t0].[Contents], [t0].[Active],
FROM [dbo].[Courses] AS [t0]
WHERE ([t0].[Title] LIKE '%word%') OR ([t0].[Contents] LIKE %word%) OR
([t0].Title] LIKE '%excel%') OR ([t0].[Contents] LIKE %excel%)
Notice there is no single Quote for the "Contents" field which is a Text field in the database.
Is there any easy way to build WHERE statement and attach it with query? Does anyone know how I can do this without PredicateBuilder?
Thanks in advance.
Since you are working w/ LINQ I suppose you are working against a LINQ-to-SQL data context right? I don't have a spare DataContext lying around to test this, but this should give you some ideas.
I don't know if it will work against data context though, but most of these are pretty basic stuff (chaining OR operator and Contains method call) so it shouldn't cause problem when the query translates to SQL.
First I create a custom function that would build my predicate:
Func<string, Func<DataItem, bool>> buildKeywordPredicate =
keyword =>
x => x.Title.Contains(keyword)
|| x.Contents.Contains(keyword);
This is a function which takes a single string keyword and then return another function which takes a DataItem and checks it against the keyword.
Basically, if you pass in "Stack", you'll get a predicate: x => x.Title.Contains("Stack") || x.Contents.Contains("Stack").
Next, since there are many possible keywords and you need to chain it with an OR operation, I create another helper function to chain 2 predicates together with an OR
Func<Func<DataItem,bool>, Func<DataItem, bool>, Func<DataItem, bool>> buildOrPredicate =
(pred1, pred2) =>
x => pred1(x) || pred2(x);
This function takes 2 predicates and then join them up with an OR operation.
Having those 2 functions, I can then build my where predicate like this:
foreach (var word in keywords) {
filter = filter == null
? buildKeywordPredicate(word)
: buildOrPredicate(filter, buildKeywordPredicate(word));
}
The first line inside the loop basically checks if the filter is null. If it is, then we want a simple keyword filter built for us.
Else if the filter is not null, we need to chain existing filters with an OR operation, so we pass the existing filter and a new keyword filter to buildOrPredicate to do just that.
And then we can now create the WHERE part of the query:
var result = data.Where(filter);
Passing in the complicated predicate we've just built.
I don't know if this will different from using PredicateBuilder but since we are deferring query translation to the LINQ-to-SQL engine, there should not be any problems.
But as I said, I havn't tested it against a real data context, so if there's any problems you can write in the comments.
Here's the console app that I built to test: http://pastebin.com/feb8cc1e
Hope this helps!
EDIT: For a more generic and reusable version which involves properly utilizing the Expression Trees in LINQ, check out Thomas Petricek's blog post: http://tomasp.net/articles/dynamic-linq-queries.aspx
As predicate builder doesn't know the DB type of the property the Contains method is called on, I guess this might be a problem inside linq to sql. Have you tried with a normal query (not with predicate builder) and a TEXT column with Contains?