Why Does My mgo FindById Query Return Zero When Data Exists?

Find by ID in MongoDB using mgo

Finding data by its ID in MongoDB using mgo is a common operation. However, issues can arise when trying to retrieve data that is known to exist, yet the query returns an empty result. This article explores the potential causes for this issue and provides solutions based on the provided question and answer.

In the question, the user attempts to retrieve data using the FindId method, passing the ID as a hexadecimal string. However, the returned value is always 0. This can occur for two reasons:

1. Incorrect usage of FindId: FindId should be used with the raw ID value, not the hexadecimal representation. Replace bson.ObjectIdHex("58593d1d6aace357b32bb3a1") with bson.ObjectId("58593d1d6aace357b32bb3a1").
2. Mismatched field name: The ID field in the MongoDB document may have a different name than the expected IdCookie field in the struct. Use struct tags to specify the correct field mapping, e.g., bson:"myid".

To optimize the database connection, it is recommended to connect to the MongoDB server once and reuse the session instead of repeatedly establishing connections.

By addressing these potential issues, the user should be able to successfully find data by ID using mgo.

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