How to Construct Nested Logical Operators in MongoDB Queries with Go Driver?

Querying MongoDB with Nested Logical Operators

When writing complex MongoDB queries, it becomes necessary to employ nested logical operators such as OR within AND or vice versa. However, the official MongoDB driver for Go presents challenges when constructing such queries.

The issue arises when trying to create a layered query filter using bson.D, which expects bson.E elements. To achieve nested OR/AND logic, one might attempt to nest bson.M within bson.D, as seen in the following example:

filter := bson.M{"$and": bson.D{{"p", 10}, bson.M{"$or": bson.D{{"s", 30}, {"a", 1}}}}}

However, this approach results in an error: "cannot use primitive.M literal (type primitive.M) as type primitive.E in slice literal."

The correct approach involves using an array (bson.A) for $or and omitting the explicit $and operator (which is implied by default). Here are three valid options for creating the nested filter:

// Option 1
filter := bson.D{
    {"p", 10},
    {"$or", bson.A{
        bson.D{{"s", 30}},
        bson.D{{"a", 10}},
    }},
}

// Option 2
filter = bson.D{
    {"p", 10},
    {"$or", bson.A{
        bson.M{"s": 30},
        bson.M{"a": 10},
    }},
}

// Option 3
filter := bson.M{
    "p": 10,
    "$or": bson.A{
        bson.M{"s": 30},
        bson.M{"a": 10},
    },
}

These filters will correctly represent the nested logical expressions and can be used to retrieve data from a MongoDB collection.

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