Example 6 – Searching an Existing List (Of Type) Using LINQ to Objects. In this example, a typed list is created (as in the previous example) using LINQ to SQL, populated, and then the returned typed list is queried using LINQ to Objects. LINQ to SQL does not give you a way to specify a set-based update against the database. The only way to update multiple entities/rows is to retrieve, modify and update them via individual SQL UPDATE statements when you call SubmitChanges. You can, however, use SQL directly to do this.

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LINQ to SQL does not give you a way to specify a set-based update against the database. The only way to update multiple entities/rows is to retrieve, modify and update them via individual SQL UPDATE statements when you call SubmitChanges. You can, however, use SQL directly to do this. Using linq to update items in a list collection hi, i have a LIST and a dataset. I'm using LINQ to join the 2 data objects together and my final result is i want to update the items in the list with linq joined records.

Is there a way to do the following using LINQ?

To clarify, I want to iterate through each object in a collection and then update a property on each object.

My use case is I have a bunch of comments on a blog post, and I want to iterate through each comment on a blog post and set the datetime on the blog post to be +10 hours. I could do it in SQL, but I want to keep it in the business layer.

Peter Mortensenlomaxxlomaxx

16 Answers

While you can use a ForEach extension method, if you want to use just the framework you can do

The ToList is needed in order to evaluate the select immediately due to lazy evaluation.

Amirhossein MehrvarziCameron MacFarlandCameron MacFarlandAdi LesterΕ Г И І И ОΕ Г И І И ОSnake Eyes

I actually found an extension method that will do what I want nicely

lomaxxlomaxx

Use:

I am not sure if this is overusing LINQ or not, but it has worked for me when wanting to update a specific items in the list for a specific condition.

Peter Mortensen

There is no built-in extension method to do this. Although defining one is fairly straight forward. At the bottom of the post is a method I defined called Iterate. It can be used like so

Iterate Source

JaredParJaredPar

I've tried a few variations on this, and I keep going back to this guy's solution.

Again, this is somebody else's solution. But I've compiled the code into a small library, and use it fairly regularly.

I'm going to paste his code here, for the off chance that his site(blog) ceases to exist at some point in the future. (There's nothing worse than seeing a post that says 'Here is the exact answer you need', Click, and Dead URL.)

granadaCoder

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granadaCoder

No, LINQ doesn't support a manner of mass updating. The only shorter way would be to use a ForEach extension method - Why there is no ForEach extension method on IEnumerable?

Aaron PowellAaron PowellAnthonyWJonesAnthonyWJones

You can use LINQ to convert your collection to an array and then invoke Array.ForEach():

Obviously this will not work with collections of structs or inbuilt types like integers or strings.

Tamas CzinegeTamas Czinege

I wrote some extension methods to help me out with that.

I am using it like this:

For reference the argument check:

Although you specifically asked for a linq-solution and this question is quite old I post a non-linq-solution. This is because linq (=lanuguage integrated query) is ment to be used for queries on collections. All linq-methods don´t modify the underlying collection, they just return a new one (or more precise an iterator to a new collection). Thus whatever you do e.g. with a Select doesn´t effect the underlying collection, you simply get a new one.

Of course you could do it with a ForEach (which isn´t linq, by the way, but an extension on List<T>). But this literally uses foreach anyway but with a lambda-expression. Apart from this every linq-method internally iterates your collection e.g. by using foreach or for, however it simply hides it from the client. I don´t consider this any more readable nor maintainable (think of edit your code while debugging a method containing lambda-expressions).

Having said this shoulnd´t use Linq to modify items in your collection. A better way is the solution you already provided in your question. With a classic loop you can easily iterate your collection and update its items. In fact all those solutuions relying on List.ForEach are nothing different but far harder to read from my perspective.

So you shouldn´t use linq in those cases where you want to update the elements of your collection.

HimBromBeereHimBromBeere

You can use Magiq, a batch operation framework for LINQ.

Peter Mortensen

I assume you want to change values inside a query so you could write a function for it

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But not shure if this is what you mean.

StormenetStormenet

Vb Net Linq

Suppose we have data like below,

and if we want to modify the list and replace the existing values of the list to modified values, then first create a new empty list, then loop through data list by invoking modifying method on each list item,

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I had a list

where Myclass is

items in li looks like

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and want result which looks like this

my code gives error can you please tell how i do this

Co. AdenCo. Aden

7 Answers

Kamil BudziewskiKamil BudziewskiBaldrickBaldrick

If you really want to use linq, you can do something like this

or

This assumes that there are only 3 types of name. I would externalize that part into a function to make it more manageable.

SmeegsSmeegs

Try this:

All values are updated in one line of code and you browse the List only ONE time. You have also a way to set a default value.

SantoshSantoshFindOut_Quran

Update List Using Linq

FindOut_Quran

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