我有一个名为“交易”的集合。这是集合的结构:
{
"TradeId": 1234,
"Products": [
{
"Name": "Test product",
"Offers": [
{
"SupplierName": "John Smith",
"OfferPrice": 12345.6
}],
"Requests": [
{
"CustomerName": "Anna Doe",
"RequestPrice": 28574.5
}]
}]
}
我只需要获取指定交易的“要约”数组,即可按产品名称进行过滤。到目前为止,这是我所做的:
var filteredTrade = await _tradesCollection.Find(
x => x.TradeId == 1234)
.Project<Trade>(Builders<Trade>.Projection.ElemMatch(
x => x.Products,
i => i.Name == "Test product"))
.SingleOrDefaultAsync();
这将按预期过滤产品名称。但是,查询还会获取整个请求集合。有什么办法可以使 only 仅提供报价集合或以某种方式排除请求集合?
答案 0 :(得分:1)
您需要使用Aggregation Framework来投影具有多层嵌套数组的文档。在mongo shell中,您可以尝试以下代码:
db.col.aggregate([
{
$match: { TradeId: 1234 }
},
{
$unwind: "$Products"
},
{
$match: { "Products.Name": "Test product" }
},
{
$project: {
_id: 0,
Offers: "$Products.Offers"
}
}
])
打印:{ "Offers" : [ { "SupplierName" : "John Smith", "OfferPrice" : 12345.6 } ] }
可以转换为以下C#代码(返回类型Product
的列表):
var project = new BsonDocumentProjectionDefinition<BsonDocument>(
BsonDocument.Parse("{ Offers: \"$Products.Offers\", _id: 0 }"));
var q = Col.Aggregate()
.Match(x => x.TradeId == 1234)
.Unwind<Trade>(x => x.Products)
.Match(x => x["Products.Name"] == "Test product")
.Project(project)
.As<Product>()
.ToList();