LINQ 面试题与答案
问题 6. Explain the usage of 'group by' in LINQ.
'Group by' is used to group elements based on a specific key. It is often used in conjunction with aggregate functions like Count, Sum, etc.
Example:
var result = from p in products group p by p.Category into g select new { Category = g.Key, Count = g.Count() };
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问题 7. What is the purpose of the 'orderby' clause in LINQ?
The 'orderby' clause is used to sort the elements of a sequence in ascending or descending order.
Example:
var query = from x in myList orderby x descending select x;
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问题 8. Explain the use of 'join' in LINQ.
'Join' is used to combine elements from two or more collections based on a related key.
Example:
var result = from p in products join c in categories on p.CategoryID equals c.CategoryID select new { Product = p.Name, Category = c.Name };
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问题 9. What is the purpose of the 'SingleOrDefault' method in LINQ?
'SingleOrDefault' returns the only element of a sequence or a default value if the sequence is empty. It throws an exception if there is more than one element.
Example:
var item = myList.SingleOrDefault(x => x.ID == 5);
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问题 10. Explain the concept of 'query syntax' and 'method syntax' in LINQ.
'Query syntax' is the SQL-like syntax used in LINQ queries, while 'method syntax' involves using extension methods and lambda expressions to achieve the same results.
Example:
Query Syntax: var result = from x in myList where x > 5 select x;
Method Syntax: var result = myList.Where(x => x > 5);
Method Syntax: var result = myList.Where(x => x > 5);
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