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Questions tagged [linq]

Language Integrated Query (LINQ) is a Microsoft .NET Framework component that adds native data querying capabilities to .NET languages, although ports exist for Java, PHP, JavaScript and ActionScript.

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41 views

How to join two sets of 6 tables and select the list into another set of 6 tables

A1 |__A2 |__A3 |__A4 |__A5 B1 |__B2 |__B3 |__B4 |__B5 C1 |__C2 |__C3 |__C4 |__C5 Given a list of A and a list of B, we want to "join" ...
6
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4answers
420 views

Replacing Linq Methods with Extension Methods

So, I've fallen into the fad trap, and started replacing a large amount of linq queries with extension methods. For example: orders.Where(o => o.Status == ShippedStatus.Shipped).Select(o => o....
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13answers
11k views

Is it unreasonable to expect Any() *not* to throw a null reference exception?

When you create an extension method you can, of course, call it on null.But, unlike an instance method call, calling it on null doesn't have to throw a NullReferenceException -> you have to check and ...
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1answer
165 views

Which is best software design for heavy query based app

I am in charge of design an application (.NET) that has these features: It´s a desktop app (maybe in the future will be web-based) It´s functionality is to provide users analyzed data retrieved ...
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6answers
3k views

What advantage was gained by implementing LINQ in a way that does not cache the results?

This is a known pitfall for people who are getting their feet wet using LINQ: public class Program { public static void Main() { IEnumerable<Record> originalCollection = ...
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1answer
210 views

Reactive Programming in C# - how to roll my own?

I've been using Linq for a while unknowingly that it uses a Reactive pattern that I'm quite fond of. I'd like to roll my own function in that pattern but wasn't sure if it's appropriate and also ...
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3answers
80k views

Null or empty object when LINQ to Entities query returns nothing

Say I have a LINQ query like this: application = CreditDatabase .Applications .Select(Mapper.Map<Application>) .Where(c =...
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1answer
2k views

Unit tests: deferred assertions with Linq

Is it ok to add deferred assertions like this var actualKittens = actualKittens.Select(kitten => { Assert.IsСute(kitten); return kitten }); Why? So I can iterate just once even with ...
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1answer
3k views

How do you create a Linq IQueryable Where query with string predicate and params object[] arguments

I would like to create a IQueryable Where method as shown below: public static IQueryable Where(this IQueryable source, string predicate, params object[] values) {} So instead of Where(u => u....
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5answers
6k views

Import large csv files

I've been tasked to query 2 large csv files which are roughly 1 GB in size each. The files contain related data, so file one may contain a list of order numbers, Order Dates, etc and the file may ...
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2answers
235 views

Name for a Chainable ForEach [closed]

Linq has a method Select, which takes a Func<TIn, TOut> and maps it over an iterable. I'm trying to come up with a good name for a method that takes an Action <TIn>, transforms it to ...
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3answers
1k views

What is the reasoning behind naming of the .NETs Select (Map) and Aggregate (Reduce)?

In other programming languages, I have seen Map and Reduce, and those are cornerstones of functional programming. I could not find any reasoning or history why LINQ has Aggregate (same as Reduce) and ...
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1answer
1k views

Efficient way in comparing two lists

I have created two lists of objects: One is records from an xml and the other is records from the database. The rule is check if the record from an xml exist in the database then exclude. I have ...
0
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1answer
662 views

Create an item in two different table with auto-increment C# SQL [closed]

First of all, let me apologize because I know my question will be very confusing since my English is pretty bad. I am working on a project for a company, mainly create a system to take care for ...
4
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3answers
315 views

How to avoid the LoadBy pattern?

In our codebase for a sophisticated system controlling many aspects of businesses, we have a certain unwritten law to not fudge around in code with complicated SQL, instead writing it into a function ...
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2answers
6k views

how to do temporary tables in Linq to Entity Framework

Our application queries the database primarily using Linq queries backed by Entity Framework but we sometimes call legacy stored procedures. Sometimes we want to replace an existing stored procedure ...
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0answers
1k views

The best way to convert Dynamic SQL to C#/Linq while joining multiple tables

I am trying to find the best way to convert the following dynamic SQL snippet to C# / Linq. The question is complicated by the use of multiple tables within the dynamic SQL. I've examined the ...
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1answer
4k views

Should I write complex Linq queries?

I often find complex Linq queries that span over 10-15 lines in our code base. I find such queries hard to understand and impossible to debug. I've tried to split the query to smaller parts, but it's ...
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1answer
590 views

C# Constructor and private LINQ to SQL members

I am extending an application I have developed so that it is more broadly useful for multiple jobs, rather than the single job I created it for. There are a number of tables that I get from SQL ...
0
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1answer
4k views

Most efficient LINQ result for Contains() query

I currently use the following: var result = list.Union(otherList).SelectMany(l => l.children).ToList() foreach(var child in lotsOfChildren){ something = result.Contains(child) } I only use ...
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1answer
916 views

Portable Data in C# App

I have developed a C# front end app for management of an SQL Database for the purposes of document control. The project this database is for has several consultants and a client spread in a variety ...
3
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1answer
3k views

How to write unit tests for a piece of code that has a data context?

I am new to unit testing and using Microsoft's unit testing library for following piece of code. When I execute the code normally it executes fine, however when I run unit test written for this code I ...
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1answer
927 views

Good design pattern for linq to sql

I currently have a linq to sql project that was used for one project and not much work was put into it, only the generated context and entities were used. Since then the project has started to become ...
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1answer
421 views

More appropriate to validate a dependency filter parameter by mock+stub or by expression compile?

My lead is enforcing TDD on our project. He says he's following Uncle Bob (Robert Martin) and SOLID principles. One of the rules he's reinforcing is what I call "the single cog rule"--there should be ...
2
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1answer
2k views

Why does Linq to Entity Sum return null when the result set is empty?

There are quite a few questions on Stack Overflow about the Linq to Entity / Linq to SQL Sum extension method, about how it returns null when the result set is empty: 1, 2, 3, 4, 5, 6, 7, and many ...
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1answer
4k views

There's a most performant way to check that a collection has exactly 1 element?

I came up with this solution : if (Take(2).Count() == 1) is there any more performance solution (or better syntactical sugar) to do this check ? I want a performance way because this will be an ...
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2answers
2k views

Is it faster to query using linq-to-entities or a data adapter?

I'm creating an MVC application in VS2012 and I reverse-engineered the models from existing Oracle tables. The tables are part of a MASSIVE database. Besides the main tables that I need to insert, ...
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1answer
925 views

Simplifying data search using .NET

An example on the asp.net site has an example of using Linq to create a search feature on a Music album site using MVC. The code looks like this - public ActionResult Index(string movieGenre, string ...
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2answers
101k views

foreach in list or foreach in list.where [duplicate]

I don't know what to call this question. This is my example: foreach (var item in lstItem.Where(item => stock.ItemCode == item.ItemCode)) { stock.ItemName = item.ItemName; stock....
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1answer
200 views

Preference to see if a field's value was changed js or linq object?

We have some requirements to send emails when various field values are changed in our system. It's an asp.net system using linq to sql with javascript/jquery. Is it preferred to check if a value ...
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2answers
697 views

TDD - Making assertions about C# Expression trees

How would you unit test the PerformUpdate method in the sample below? This is a (very) simplified version of some code that performs updates against a database where the schema is dynamic and ...
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3answers
2k views

Optimal way to implement this specific lookup table in C#?

I want to create a lookup table for this data: The "input variables" (what is used to "lookup") are 4 different doubles that can each take on 1 of 200 numbers (the numbers range from 1-1000 but there ...
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1answer
2k views

which sorting algorithms is using OrderBy

I am litle curious about what sorting algorithm is using OrderBy (linq to objects). quicksort? heapsort? introspective sort ? As i see in MSDN documentation List.Sort is using introspective sort: ...
0
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1answer
348 views

C# LinqExtensions implement multiple inheritance

According to WikiPedia "Some languages do not support mixins on the language level, but can easily mimic them by copying methods from one object to another at runtime, thereby "borrowing" the mixin's ...
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3answers
4k views

Is it possible to implement an infinite IEnumerable without using yield with only C# code?

Motivation The main idea is to explore and understand the limits of how far one can go with the basic LINQ primitives (Select, SelectMany, Concat, etc.). These primitives can all be considered ...
13
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4answers
2k views

Is linq more efficient than it appears on the surface?

If I write something like this: var things = mythings .Where(x => x.IsSomeValue) .Where(y => y.IsSomeOtherValue) Is this the same as: var results1 = new List<Thing>(); foreach(...
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1answer
1k views

Using Dynamic LINQ to get a filter for my Web API

We are considering using the Dynamic.CS linq-sample included in the "Samples" directory of visual studio 2008 for our WebAPI project to allow clients to query our data. The interface would be ...
3
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2answers
3k views

Extracting lambda expressions from linq queries and readability

Every now and then when I have a complex lambda, I do something like this: Func<SomeObject, bool> equals = o => o.ID == someID && o.Name == someName && IsAdd || ... var ...
13
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5answers
14k views

XSLT and possible alternatives [closed]

I had a look at XSLT for transforming one XML file into another one (HTML, etc.). Now while I see that there are benefits to XSLT (being a standardized and used tool) I am reluctant for a couple of ...
2
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4answers
494 views

Why should IQueryProvider implementations throw NotSupportedExceptions?

Searching the web, we can find plentiful examples of various ORMs (nHibernate, EF, LinqToSql, etc.) that implement but don't actually support the full IQueryable<T> interface, throwing ...
13
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1answer
14k views

Why is imperative programming preferred over functional programming? [closed]

Background: I am proponent of functional programming who works at a VB.NET shop where the prevailing mental model is imperative programming. Being that foundation of our system is WinForms I can ...
2
votes
1answer
792 views

Is it okay to convert dataset from stored procedure to IEnumerable

So, I am working on a project with a team and we are using Entity Framework. We basically want to use linq to entities, and not use stored procedures. I use quite a bit of lists and IEnumerables and ...
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2answers
1k views

Style for creating IEnumerable unions [closed]

There isn't any cool LINQ sugar for creating unions. The Enumerable.Union() method is usually called like this: var bigList = list1.Union(list2); The alternative is to call Enumerable.Union() which ...
12
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3answers
2k views

What problem domain is LINQ made for?

Each time I see a question posted on Stack Overflow on C#, I see at least one or two answers posted that solve a problem with LINQ. Usually people with very high reputation seem to use LINQ like pros. ...
4
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2answers
11k views

Is it better to create a stored procedure or entities to get to the data I need?

I just jumped into a new project with a new company using Entity Framework and ASP.NET MVC 4. I am no expert on Entity Framework, but I think I have a decent grasp of how to use it. From what I can ...
83
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5answers
107k views

for vs. foreach vs. LINQ

When I write code in Visual Studio, ReSharper (God bless it!) often suggests me to change my old-school for loop in the more compact foreach form. And often, when I accept this change, ReSharper goes ...
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1answer
943 views

Algorithm to optimize grouping

I would like to know if there's a known algorithm or best practice way to do the following: I have a collection with a subcollection, for example: R1 R2 R3 -- -- -- M M M N N L L A What i ...
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5answers
552 views

Using 'new' in a projection?

I wish to project a collection from one type (Something) to another type (SomethingElse). Yes, this is a very open-eneded question, but which of the two options below do you prefer? Creating a new ...
2
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1answer
4k views

Nesting Linq-to-Objects query within Linq-to-Entities query –what is happening under the covers?

var numbers = new int[] { 1, 2, 3, 4, 5 }; var contacts = from c in context.Contacts where c.ContactID == numbers.Max() | c.ContactID == numbers.FirstOrDefault() ...
2
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1answer
365 views

Are elements returned by Linq-to-Entities query streamed from the DB one at the time or are they retrieved all at once?

Are elements returned by Linq-to-Entities query streamed from the database one at the time ( as they are requested ) or are they retrieved all at once: SampleContext context = new SampleContext();...