How can I do SELECT UNIQUE with LINQ?

Naughtily nagging Lambda expressions and playful LINQ method syntax

Lambda expressions and the LINQ method syntax afford you the latitude to create intricate sorting and filtering requisites within your queries. So, if your mission is to select unique values based on just one lonesome property and then sort 'em up in alphabetical order, here's a cracking tip:

var uniqueSortedItems = context.Entities
                               .Select(e => e.Property) //Why take everyone when you can handpick!
                               .Distinct() //Because no one likes a copycat!
                               .OrderBy(p => p) //Alpha Order! Just like your elementary school roll call!
                               .ToList();


Bear in mind that when you're sorting post Distinct(), its performance could seem lethargic, especially with those fussy large datasets.

Hands-on table structures and the relational wisdom

Your deep dive in understanding your database structure and the interlaced relationships between tables is a paramount part of writing your LINQ queries. Do a quick sanity check on how your query might need to play nicely with joining entities or tables, as these could unsettle the uniqueness of your retrieved records.

Confronting the typical LINQ beasties

Ever bumped into confounding LINQ errors such as type arguments cannot be inferred? These tend to crop up from complex queries where the compiler isn't on speaking terms with the involved types. A quick overview of your query structure and perhaps a friendly nod towards the var keyword or explicit type definition could help you clear this fog:

var uniqueProducts = context.Products
                            .Where(p => p.Category == "Toys") //Only the choicest of Toys!
                            .Select(p => new { p.Id, p.Name }) //The Id and Name duo!
                            .Distinct(); //Putting an end to the clone wars!


Power-packing grouping, and suave sorting

Multitasking property grouping

Often, singling out uniques can ride on the shoulders of multiple properties. Let's take a leap of grouping faith:

var uniqueCategories = context.Products
                              .GroupBy(p => new { p.Category, p.Supplier }) //Double trouble!
                              .Select(g => g.Key) //Keys, ever the unique puzzle pieces!
                              .ToList();


Efficient eyeballing with select before sorting

To dodge performance roadblocks, especially with larger datasets, project your needed properties before the assault on sorting:

var efficientUniqueSorted = context.Orders
                                   .Select(o => o.CustomerID) //Picking out just the customers
                                   .Distinct() //Because every customer is unique!
                                   .OrderBy(id => id) //Rolling out the red carpet in Order!
                                   .ToList();


Testing trenches

Experience is the best tutor! Experiment on a variety of datasets to be sure your LINQ queries hold up to your expected outcomes. Tools like LINQPad can be your playground to explore various scenarios, leading you to the treasure trove of perfect queries.

Tapping community brainpower

Sometimes, it's the alternative perspectives and collective knowledge from the developer community that helps in ironing out the wrinkles of complex requirements or elusive bugs. Remember, in the world of code, it's teamwork for the win!