常见的Linq /标准查询运算符错误/错误步骤？

Question

对于不是来自函数式编程背景的程序员,是否有错误要避免？

Answer 1

人们倾向于犯的最大错误是误解了LINQ查询的懒惰和评估规则:

查询是惰性的:在迭代它们之前它们不会被执行:

// This does nothing! No query executed!
var matches = results.Where(i => i.Foo == 42);

// Iterating them will actually do the query.
foreach (var match in matches) { ... }

此外,结果不会缓存.每次迭代它们时都会计算它们:

var matches = results.Where(i => i.ExpensiveOperation() == true);

// This will perform ExpensiveOperation on each element.
foreach (var match in matches) { ... }

// This will perform ExpensiveOperation on each element again!
foreach (var match in matches) { ... }

底线:知道您的查询何时执行.