63 lines
2.4 KiB
Markdown
63 lines
2.4 KiB
Markdown
---
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title: LINQ
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---
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# LINQ (Language Integrated Query)
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LINQ (Language Integrated Query) is a Microsoft programming model and methodology that essentially adds formal query capabilities into Microsoft .NET-based programming languages. LINQ offers a compact, expressive, and intelligible syntax for manipulating data. The real value of LINQ comes from its ability to apply the same query to an SQL database, a DataSet, a list, a dictionary, etc.
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## Example
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LINQ can be used to filter, transform, search data and a lot more complex tasks. Let's say we have the following list of objects:
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```csharp
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var fruits = new List<Fruit>() {
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new Fruit() { Id = 1, Name = "Orange", Color = "Orange", Quantity: 3 },
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new Fruit() { Id = 2, Name = "Strawberry", Color = "Red", Quantity: 12 },
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new Fruit() { Id = 3, Name = "Grape", Color = "Purple", Quantity: 25 },
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new Fruit() { Id = 4, Name = "Pineapple", Color = "Yellow", Quantity: 1 },
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new Fruit() { Id = 5, Name = "Apple", Color = "Red", Quantity: 5 },
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new Fruit() { Id = 6, Name = "Mango", Color = "Yellow", Quantity: 2 }
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}
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```
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Then we can do things like:
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```csharp
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// Get the name of the first fruit
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var firstName = fruits.Select(f => f.Name).First(); // Orange
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// Count how many fruits are red
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var qntRed = fruits.Where(f => f.Color == "Red").Count(); // 2
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// Create a list of yellow fruits
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var yellowFruits = fruits.Where(f => f.Color == "Yellow").ToList(); // { Pineapple, Mango }
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// Orders list by quantity from most to least
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var orderedFruits = fruits.OrderByDescending(f => f.Quantity).ToList(); // {Grape, Strawberry, Orange, Apple, Mango, Pineapple}
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// Sum the quantity of fruits
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var quantity = fruits.Sum(f => f.Quantity); // 53
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// Check if there are any green fruits
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var hasGreen = fruits.Any(f => f.Color == "Green"); // false
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// Group fruits by color into a dictionary
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var fruitsByColor = fruits.GroupBy(g => g.Color).ToDictionary(k => k.Key, v => v.ToList()); // Dictionary of list of fruits by color
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// linq operations can be concatenated and are not performed as long as data is needed
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var logs = new List<Log>;
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if (filterBySeverity)
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logs = logs.Where(p => p.Severity == severity);
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//IQueryable
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if (filterByUser)
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logs = logs.Where(p => p.User == user);
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//IQueryable
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result = logs.ToList();
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//List<log>
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```
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