Linq 延遲執行

使用linq時，其中乙個重要概念就是延遲執行，所有的謂詞求值需要等到觸發時才會被呼叫。在宣告時，它們是不執行的，除非呼叫lambda表示式，造成其中的**開始執行，否則不會被執行。如果lambda表示式執行的代價比較高(如呼叫資料庫，密集計算等)，那麼為了優化**，通過使用」to***」方法來轉換為集合方式，減少lambda表示式的執行。但轉換後會造成整個結果都載入到記憶體(在此之前可能駐留在乙個資料庫或檔案中)。除此之外，」to***」方法會建立基礎資料的」快照」，需保證在查詢」to***」方法的結果時，不會返回新的結果。測試**如下：

public class patent 
public string yearofpublication 
public long inventorids 
public override string tostring()
()",title,yearofpublication);}};
public class inventor
public string name 
public string city 
public string state 
public string country 
public override string tostring()
(,)",name,city,state);}};
public static class patentdata
,new inventor() ,
new inventor() ,
new inventor() 
};public static readonly patent patents = new patent 
},new patent() 
},new patent() 
},new patent() 
},new patent() 
},new patent() 
},new patent() 
},new patent() 
},};
};class program
}static void main(string args)
return result;});
console.writeline("1. patents prior to the 1900s are:");
foreach (patent patent in patents)
console.writeline();
console.writeline("2. a second listing of patents prior to the 1900s:");
console.writeline(" there are patents prior to 1900.",patents.count());
console.writeline();
console.writeline("3. a third listing of patents prior to the 1900s:");
patents = patents.toarray();
console.write(" there are ");
console.writeline(" patents prior to 1900.",patents.count());
console.readline();
}}

執行結果如下:

1. patents prior to the 1900s are:
phonograph(1877)
hello in patent.
kinetoscope(1888)
hello in patent.
electrical telegraph(1837)
hello in patent.
steam locomotive(1815)
hello in patent.
2. a second listing of patents prior to the 1900s:
phonograph(1877)
kinetoscope(1888)
electrical telegraph(1837)
steam locomotive(1815)
there are 4 patents prior to 1900.
3. a third listing of patents prior to the 1900s:
phonograph(1877)
kinetoscope(1888)
electrical telegraph(1837)
steam locomotive(1815)
there are 4 patents prior to 1900.

具體**分析詳見<

Linq 延遲執行

Linq基礎知識之延遲執行

LINQ延遲查詢

延遲查詢 LINQ

Linq 延遲執行

Linq基礎知識之延遲執行

LINQ延遲查詢

延遲查詢 LINQ

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