hop是用來吧transformation和job連接起來的。數據流動的方向在hop里是通過箭頭表示的。hop可以設置為有效或者無效。

下面介紹主要是以下內容：

Transformation Hops
Job Hops
Creating a Hop
Splitting a Hop
Loops
Mixing Rows-Trap Detector
Transformation Hop Colors

Transformation Hops：

如果在轉換中，hop是無效的，那么，在數據流方向上，其后的單元將得不到任何數據。從而導致結果是無效的。比如，在無效hop的下一個轉換，單擊get fields，講啥都得不到。

job hops

Besides the execution order, a hop also specifies the condition on which the next job entry will be executed. You can specify the evaluation mode by right clicking on the job hop:

"Unconditional" specifies that the next job entry will be executed regardless of the result of the originating job entry.
"Follow when result is true" specifies that the next job entry will only be executed when the result of the originating job entry was true, meaning successful execution, file found, table found, without error, evaluation was false, ...
"Follow when result is false" specifies that the next job entry will only be executed when the result of the originating job entry was false, meaning unsuccessful execution, file not found, table not found, error(s) occurred, evaluation was false, ..

create a hop

Create a new hop between two steps using one of the following options:

Drag the Graphical View between two steps while holding down the middle mouse button
Drag the Graphical View between two steps while pressing the <SHIFT>key and using the left mouse button
Right click and select New Hop to select two steps in the tree
Use <CTRL> + left-click to select two in the graphical view; the right-click on the step and choose New Hop

Mixing Rows-Trap Detector

hop的顏色標識

Hop Color	Meaning
Green	Distribute rows: if multiple hops are leaving a step, rows of data will be evenly distributed to all target steps.
Red	Copies rows: if multiple hops are leaving a step, all rows of data will be copied to all target steps.
Yellow	Provides info for step, distributes rows
Magenta	Provides info for step, copies rows
Gray	The hop is disabled.
Black	The hop has a named target step.
Blue	Candidate hop using middle button + drag
Orange (Dot line)	The hop is never used because no data will ever go there.
Red (Bold Dot line)	The hop is used for carrying rows that caused errors in source step(s).

總結

以上是生活随笔為你收集整理的kettle用户手册（3：创建hops）的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。