在libxml2中使用XPath选择节点

我有一个类似于以下内容的XML文档

<library>
  <artist name="a">
   <album name="1"></album>
   <album name="2"></album>
  </artist>
  <artist name="b">
   <album name="8"></album>
   <album name="9"></album>
  </artist>
</library>`

此XPath查询仅返回艺术家a下的相册，即相册1和2。但是，

context.eval（“/library/artist[@name=“b”]/album”）

正在返回艺术家b下的所有相册

上述代码的python等价物正在生成所需的结果

doc = libxml2.parseFile("data.xml")
ctxt = doc.xpathNewContext()
res = ctxt.xpathEval("//album")

---

Vala代码有什么问题？

首先，您应该通过检查

object->type==Xml.ObjectType.NodeSet来检查返回的对象是否是节点集

接下来，只返回结果节点集中的第一项。有
nodeset->length（）
项

void main() {
    var document = Xml.Parser.parse_file ("file.xml");
    run_query("//album", document);
    run_query("/library/artist[@name=\"b\"]/album", document);
}

void run_query(string query, Xml.Doc* document) {
    stdout.printf("Query: %s\n", query);
    Xml.XPath.Context context;
    unowned Xml.XPath.Object *object;

    context = new Xml.XPath.Context(document);
    object = context.eval(query);
    assert(object->type == Xml.XPath.ObjectType.NODESET);

    if(object->nodesetval->is_empty()) {
        stdout.printf("empty");
        return;
    }

    for (var i = 0; i < object->nodesetval->length(); i++) {
        var node = object->nodesetval->item(i);
        stdout.printf("node %s name=\"%s\"\n", node->name, node->get_prop("name"));
    }
}

void main() {
    var document = Xml.Parser.parse_file ("file.xml");
    run_query("//album", document);
    run_query("/library/artist[@name=\"b\"]/album", document);
}

void run_query(string query, Xml.Doc* document) {
    stdout.printf("Query: %s\n", query);
    Xml.XPath.Context context;
    unowned Xml.XPath.Object *object;

    context = new Xml.XPath.Context(document);
    object = context.eval(query);
    assert(object->type == Xml.XPath.ObjectType.NODESET);

    if(object->nodesetval->is_empty()) {
        stdout.printf("empty");
        return;
    }

    for (var i = 0; i < object->nodesetval->length(); i++) {
        var node = object->nodesetval->item(i);
        stdout.printf("node %s name=\"%s\"\n", node->name, node->get_prop("name"));
    }
}

Query: //album
node album name="1"
node album name="2"
node album name="8"
node album name="9"
Query: /library/artist[@name="b"]/album
node album name="8"
node album name="9"