mongodb query field is null
If the expression evaluates to a null value, including instances of undefined values or missing fields, returns the value of the replacement expression. The $ifNull ... , So in your provided case following query going to return all the documents with imageurl field exists and having not null value:
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 mongodb query field is null 相關參考資料
$exists — MongoDB Manual - MongoDB Documentation
When <boolean> is true, $exists matches the documents that contain the field, including documents where the field value is null . If <boolean> is false, the query ... https://docs.mongodb.com $ifNull (aggregation) — MongoDB Manual
If the expression evaluates to a null value, including instances of undefined values or missing fields, returns the value of the replacement expression. The $ifNull ... https://docs.mongodb.com How do you query for "is not null" in Mongo? - Stack Overflow
So in your provided case following query going to return all the documents with imageurl field exists and having not null value: https://stackoverflow.com How to find null documents in mongodb? - Stack Overflow
The second query looks for the existence of all the fields except the _id ... collection has documents with the keys _id , a , b and c , the query https://stackoverflow.com MongoDB query with null - w3resource
In this page we are going to discuss how null value in mongodb ... The $exist operator checks whether the particular field exist or not. https://www.w3resource.com MongoDB: How to query for records where field is null or not set ...
If the sent_at field is not there when its not set then: db.emails.count(sent_at: $exists: false}}). If its there and null, or not there at all: https://stackoverflow.com Query for Null or Missing Fields - MongoDB Documentation
The query only returns the document that does not contain the item field. Reference documentation for the $type and $exists operators. Starting in MongoDB 4.2, users can no longer use the query filter... https://docs.mongodb.com Query for Null or Missing Fields — MongoDB Manual 3.4
This page provides examples of operations that query for null values using the db.collection.find() method in the mongo shell. The examples on this page use ... https://docs.huihoo.com 查询值为Null或不存在的字段— MongoDB Manual 3.4
The name : null } query matches documents that either contain the name field whose value is null or that do not contain the name field. 给出如下查询:. http://www.mongoing.com |