Question

我在MongoDB中有以下集合：

using iTextSharp.text;
using iTextSharp.text.pdf;

Mongo Shell中的查询是什么//Create a byte array that will eventually hold our final PDF Byte[] bytes; //Boilerplate iTextSharp setup here //Create a stream that we can write to, in this case a MemoryStream using (var ms = new MemoryStream()) { //Create an iTextSharp Document which is an abstraction of a PDF but **NOT** a PDF using (var doc = new Document()) { //Create a writer that's bound to our PDF abstraction and our stream using (var writer = PdfWriter.GetInstance(doc, ms)) { //Open the document for writing doc.Open(); string finalHtml = string.Empty; // read your html by database or from a html file here and store it into finalHtml e.g. a string //XMLWorker also reads from a TextReader and not directly from a string using (var srHtml = new StringReader(finalHtml)) { //Parse the HTML iTextSharp.tool.xml.XMLWorkerHelper.GetInstance().ParseXHtml(writer, doc, srHtml); } doc.Close(); } } //After all of the PDF "stuff" above is done and closed but **before** we //close the MemoryStream, grab all of the active bytes from the stream bytes = ms.ToArray(); } //clear the response Response.Clear(); MemoryStream mstream = new MemoryStream(bytes); //define response content type Response.ContentType = "application/pdf"; //give the name of file of pdf and add in to header Response.AddHeader("content-disposition", "attachment;filename=invoice.pdf"); Response.Buffer = true; mstream.WriteTo(Response.OutputStream); Response.End();有{ "id": 123, "profile":{ "name": "name", "age":45, "wishlist": [ {"_id":1, "name":"a1"}, {"_id":2, "name":"a2"}, {"_id":3, "name":"a3"} ] } }的集合？

Answer 1

当您与一个字段匹配时，您只需使用点符号表示您的字段的路径：

> db.user.find({"profile.wishlist._id": 2})

如MongoDB documentation中所述，对于数组（如wishlist），如果数组中的任何子文档与字段值匹配，则这将匹配文档。

请注意，如果您需要与几个字段匹配，则需要使用以下任一字段：

$elemMatch如果所有匹配的字段都属于相同的子文档;
或如果各个字段不需要与同一子文档匹配，则使用点表示法表示多个字段。

请比较这两个查询的输出以掌握这一点：

> db.user.find({"profile.wishlist._id": 2, "profile.wishlist.name": "a1"})
//                                      ^                            ^^
//                              will return your document even if the was no 
//                              subdocument having both _id=2 and name=a1

> db.user.find({"profile.wishlist": {$elemMatch: { _id: 2, name: "a1"}}})
//                                                      ^         ^^
//                                         no result as there was no subdocument
//                                         matching  _both_ _id=2 and name=a1

嵌套数组中的MongoDB查询

1 个答案: