如何從mongoDB集合中的特定行（例如第6行）獲取數據？

Question

如果我在mongo集合中的數據是這樣的

{ "_id" : ObjectId("4fff9946af8c6149aed251ab"), "subject_slug" : "math", "lesson_slug" : "mat01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251ac"), "subject_slug" : "math", "lesson_slug" : "mat02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251ad"), "subject_slug" : "math", "lesson_slug" : "mat03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251ae"), "subject_slug" : "eng", "lesson_slug" : "eng01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251af"), "subject_slug" : "eng", "lesson_slug" : "eng02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b0"), "subject_slug" : "eng", "lesson_slug" : "eng03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b1"), "subject_slug" : "phy", "lesson_slug" : "phy01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b2"), "subject_slug" : "phy", "lesson_slug" : "phy02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b3"), "subject_slug" : "phy", "lesson_slug" : "phy03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b4"), "subject_slug" : "chem", "lesson_slug" : "che01" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b5"), "subject_slug" : "chem", "lesson_slug" : "che02" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b6"), "subject_slug" : "chem", "lesson_slug" : "che03" }
{ "_id" : ObjectId("4fff9946af8c6149aed251b7"), "subject_slug" : "chem", "lesson_slug" : "che04" }

如果我想要第6行中的數據而沒有循環數據。 php中是否有短代碼來獲取該行中的數據？

Answer 1

為了找到第六條記錄，您需要使用一些MongoCursor方法 ：

• sort()所以有一個特定的順序（例如_id ）
• skip()跳過許多記錄（跳過5查找第6條記錄）
• limit()限制一個結果

代碼示例：

<?php
    $mongo = new Mongo();
    $collection = $mongo->mydb->subject;

    $query = array();
    $sort  = array('_id' => 1);

    // Find the 6th record
    $doc = $collection->find($query)->sort($sort)->skip(5)->limit(1)->getNext();

    print_r($doc);
?>

樣本輸出：

Array
(
    [_id] => MongoId Object
        (
            [$id] => 4fff9946af8c6149aed251b0
        )

    [subject_slug] => eng
    [lesson_slug] => eng03
)

請注意，如果您需要跳過大量文檔，則skip()的性能可能會成為問題。 如果可能的話，更有效的選擇是使用范圍查詢。

Answer 2

看起來像是json格式的內容，該如何將它們全部讀取到一個對象中，然后json_decode到另一個對象中，以便稍后您可以讀出第六行。