Question

我需要在SQLite中存储一棵树。我在这里找到了一个非常好的SQL Server方法：

Tree structures in ASP.NET and SQL Server

触发器的概念是明确的最终前瞻性思维。

我尝试将描述的触发器翻译成SQLite

SQL Server版本：

CREATE TRIGGER dfTree_UpdateTrigger
ON dfTree
FOR UPDATE AS
-- if we've modified the parentId, then we
-- need to do some calculations
IF UPDATE (parentId) 
UPDATE child
-- to calculate the correct depth of a node, remember that
--      - old.depth is the depth of its old parent
--      - child.depth is the original depth of the node 
--          we're looking at before a parent node moved.
--          note that this is not necessarily old.depth + 1,
--          as we are looking at all depths below the modified
--          node
-- the depth of the node relative to the old parent is
-- (child.depth - old.depth), then we simply add this to the
-- depth of the new parent, plus one.
    SET depth = child.depth - old.depth + ISNULL(parent.depth + 1,0),
    lineage = ISNULL(parent.lineage,'/') + LTrim(Str(old.id)) + '/' +
                  right(child.lineage, len(child.lineage) -     len(old.lineage))
-- if the parentId has been changed for some row
-- in the "inserted" table, we need to update the
-- fields in all children of that node, and the
-- node itself                  
FROM dfTree child 
INNER JOIN inserted old ON child.lineage LIKE old.lineage + '%'
-- as with the insert trigger, attempt to find the parent
-- of the updated row
LEFT OUTER JOIN dfTree parent ON old.parentId=parent.id

我的SQLite版本到现在为止：

CREATE TRIGGER IF NOT EXISTS sc_compare_UpdateTrigger
AFTER UPDATE ON dfTree
FOR EACH ROW
BEGIN
  UPDATE child
      SET depth = child.depth - OLD.depth + IFNULL(parent.depth + 1,0),
      lineage = IFNULL(parent.lineage,'/') + LTrim(CAST(OLD.id AS TEXT)) +     '/' +
            right(child.lineage, len(child.lineage) - len(OLD.lineage))
  FROM dfTree child 
  INNER JOIN inserted OLD ON child.lineage LIKE OLD.lineage + '%'
  LEFT OUTER JOIN dfTree parent ON OLD.parentId=parent.id
END;

对于此版本，＆＃34;错误：接近＆＃34; FROM＆＃34;：语法错误＆＃34; occours。

我走在正确的轨道上？是否可以使用SQLite构建此触发器功能？

Answer 1

Sqlite UPDATE语法不支持FROM子句。另请注意，insetred触发器中没有NEW表，OLD，FOR EACH ROW行。

查询从SQL Server到SQLite的转换

1 个答案: