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Sqlite数据库存储目录结构邻接表的实现2-目录树的构建
2022-07-07 22:03:00 【kupeThinkPoem】
目录
一、概述
存储目录结构(树)是一个常见的问题,有多种解决方案。方法主要有邻接表、进阶邻接列表、改进的前序树遍历、递归查询、枚举路径、嵌套集、闭包表等。
二、数据库存储目录结构邻接表
我们将尝试的第一种也是最优雅的方法叫做“邻接表模型”或“递归方法”。这是一个很好的方法,因为你只需要一个简单的函数来遍历你的树。在我们的食品商店中,邻接表看起来像这样:
如你所见,在邻接表方法中,你保存了每个节点的“父节点”。我们可以看到‘Pear’是‘Green’的子,是‘Fruit’的子等等。根节点“Food”没有父值。为了简单起见,我使用“title”值来标识每个节点。当然,在真实的数据库中,您将使用每个节点的数字id。
三、目录树的构建
1、数据结构
最近想在数据库的某一字段里面设置多个字符串信息,如何截取其中的某个字符串?需要在数据库获取parentID这个属性进行相应的操作。
struct dirpro
{
char type;
char opType;
char parentID[32];
char rerserved[128-32-1-1];
};
struct DirProNode
{
int id;
std::string name;
std::string parId;
QLinkedList<DirProNode> children;
};
struct DirInfo
{
int id;
std::string name;
dirpro pro;
};
2、代码实现构建树
DirProNode getTree()
{
std::vector<DirInfo> vInfos =getdirproFromDb();//从数据库中读取所有的目录信息
DirProNode root;//根节点
root.id=-1;
root.parId="NULL";
root.name="root";
int nsize=vInfos.size();
std::map<std::string,DirProNode*> mapDirThink;
std::vector<bool> vecMark;
vecMark.resize(nsize);
for(int i=0;i<nsize;++i)
{
vecMark[i]=false;
}
while(true)
{
int ncount=0;
for(int i=0;i<nsize;++i)
{
if(vecMark[i])
{continue;}
DirProNode dirproNode;
if(convert(vInfos[i],dirproNode)
{
if(dirproNode.parId=="NULL" || dirproNode.parId.isEmpty())
{
root.children.push)back(dirproNode);
mapDirThink[QString::number(dirproNode.id).c_str()]=&(root.children.back());
ncount++;
vecMark[i]=true;
}
else
{
mapDirThink[dirproNode.parId]->children.push_back(dirproNode);
mapDirThink[QString::number(dirproNode.id).c_str()]=&(root.children.back());
ncount++;
vecMark[i]=true;
}
}
else
{
vecMark[i]=false;
}
}
if(ncount==0)
{break;}
}
return root;
}
四、QTreeWidget显示目录树
有了DirProNode这个数据结构,我们就可以使用先序遍历构建目录结构并在QTreeWidget中进行显示。
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