xpath查询是否具有像mysql这样的Limit选项 [英] Does xpath query has Limit option like mysql

问题描述

我想限制从xpath查询中收到的结果的数量.

I want to limit number of result I receive from xpath query.

例如:-

$info = $xml->xpath("//*[firstname='Sheila'] **LIMIT 0,100**"); 

您看到的是LIMIT 0,100.

推荐答案

您应该可以使用"//*[firstname='Sheila' and position() <= 100]"

给出以下XML:

<root> 
    <country.php desc="country.php" language="fr|pt|en|in" editable="Yes"> 
        <en/> 
        <in> 
            <cityList desc="cityList" language="in" editable="Yes" type="Array" index="No"> 
                <element0>Abu</element0>
                <element1>Agartala</element1>
                <element2>Agra</element2> 
                <element3>Ahmedabad</element3>
                <element4> Ahmednagar</element4> 
                <element5>Aizwal</element5>
                <element150>abcd</element150> 
            </cityList> 
        </in> 
    </country.php> 
</root>

您可以使用以下XPath来获取前三个城市:

You can use the following XPath to get the first three cities:

//cityList/*[position()<=3]

结果:

Node    element0    Abu
Node    element1    Agartala
Node    element2    Agra

如果要将其限制为以element开头的节点:

If you want to limit this to nodes that start with element:

//cityList/*[substring(name(), 1, 7) = 'element' and position()<=3]

请注意，后一个示例之所以有效，是因为您选择了 all cityList的子节点，因此在这种情况下，Position()可以按预期限制结果.如果cityList节点下混合了其他节点名称，则会得到不希望的结果.
例如，如下更改XML:

Note that this latter example works because you're selecting all the child nodes of cityList, so in this case Position() works to limit the results as expected. If there was a mix of other node names under the cityList node, you'd get undesirable results.
For example, changing the XML as follows:

<root> 
    <country.php desc="country.php" language="fr|pt|en|in" editable="Yes"> 
        <en/> 
        <in> 
            <cityList desc="cityList" language="in" editable="Yes" type="Array" index="No"> 
                <element0>Abu</element0>
                <dog>Agartala</dog>
                <cat>Agra</cat> 
                <element3>Ahmedabad</element3>
                <element4> Ahmednagar</element4> 
                <element5>Aizwal</element5>
                <element150>abcd</element150> 
            </cityList> 
        </in> 
    </country.php> 
</root>

并使用上面的XPath表达式，我们现在获得

and using the above XPath expression, we now get

Node    element0    Abu

请注意，我们丢失了第二和第三结果，因为position()函数以更高的优先级进行求值-就像请求给我前三个节点，现在从这些节点中给了我所有的三个节点一样"以"element"开头的节点."

Note that we're losing the second and third results, because the position() function is evaluating at a higher order of precedence - the same as requesting "give me the first three nodes, now out of those give me all the nodes that start with 'element'".

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