Question

以下是我拥有或尝试查询

的架构示例

{
    "_id" : ObjectId("5139f9468efdd10e44000024"),
    "name" : "Test Test",
    "account_activities" : [
        {
            "_id" : ObjectId("5139f9468efdd10e44000025"),
            "activity_id" : ObjectId("5139f6118efdd10e4400000e"),
            "allowance" : 100,
            "base_rate" : {
                "cents" : 80,
                "currency_iso" : "USD"
            },
            "excess_rate" : {
                "cents" : 90,
                "currency_iso" : "USD"
            },
            "quota" : 100,
            "taxable" : true,
            "description" : "",
            "sm" : 1,
            "updated_at" : ISODate("2015-07-24T16:18:50.942Z")
        }
    ],
    "account_number" : "D-061-5556",
    "active" : false,
    "balance" : {
        "cents" : 0,
        "currency_iso" : "USD"
    },
}

在运行$unwind时，我什么都没得到，有什么我做错了吗？

db.accounts.aggregate([{$unwind: "$account_activities"}, {$project: {_id: 0, name: 1, base_rate: 1}}])

我使用的是mongo shell版本2.6.12

Answer 1

db.accounts.aggregate([ {$unwind: "$account_activities"}, {$project: { _id: 0, name: 1, 'account_activities.base_rate': 1 }} ])仍在document = PDDocument.load(new File(pdfFilename)); PDFRenderer pdfRenderer = new PDFRenderer(document); int pageCounter = 0; for (PDPage page : document.getPages()) { BufferedImage bim = pdfRenderer.renderImageWithDPI(pageCounter, 300, ImageType.RGB); ImageIOUtil.writeImage(bim, pdfFilename + "-" + (pageCounter++) + ".tif", 300); }下。所以你必须按如下方式进行投影

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Mongodb $ unwind for mongoid embedded document

1 个答案: