在golang中追加数据时，如何解决第一个参数必须是切片

Question

I'm making a query on the basis of the conditions but there is a error in the appending of them the query I'm making is:-

query := bson.M{}
query["$or"] = []bson.M{}
if keyword != "" {
    query["$or"] = append(query["$or"], bson.M{"author": bson.RegEx{"(?i).*" + keyword + ".*", "i"}})
    query["$or"] = append(query["$or"], bson.M{"title": bson.RegEx{"(?i).*" + keyword + ".*", "i"}})
}
if types == "" {
    query["$or"] = append(query["$or"], bson.M{"type": bson.RegEx{"(?i).*" + types + ".*", "i"}})
}
if category == "" {
    query["$or"] = append(query["$or"], bson.M{"category": bson.RegEx{"(?i).*" + category + ".*", "i"}})
}
if tag == "" {
    query["$or"] = append(query["$or"], bson.M{"tags": bson.RegEx{"(?i).*" + tag + ".*", "i"}})
}
if len(ids) > 0 {
    query["_id"] = bson.M{"$in": ids}
}

There is problem of appending the data with the query["$or"]. The error comes out is:-

first argument to append must be slice; have interface {}

first argument to append must be slice; have interface {}

first argument to append must be slice; have interface {}

first argument to append must be slice; have interface {}

first argument to append must be slice; have interface {}

Can anyone tell me that how will I solve this problem.

Answer 1

Right now you're passing an interface{}, as you can see from the definition of bson.M. So you need to assert that to some type of slice.

You're assigning a slice of type []bson.M to the value earlier, so just assert that type. Example:

    query["$or"] = append(query["$or"].([]bson.M), bson.M{"author": bson.RegEx{"(?i).*" + keyword + ".*", "i"}})

what would probably be more readable, though, is to assign your calculated value at the end instead:

or := []bson.M{}
// ...
    or = append(or, ...)

query["$or"] = or