使用Golang动态查询mongodb

Question

I'm trying to query my mongodb database using golang (and the mgo library) with only one function, and the method I am currently using is:

er = c.Find(sel(items)).Sort("-createdAt").All(&result)

Where items is a map and the key is the name of the field I am searching inthe db, and the value is what I want to search by.

and sel() is:

func sel(query map[string]string) bson.M {
result := make(bson.M, len(query))
result[ ] = "$in"
for k, v := range query {
    result[k] = v
}
return result

currently it will return all of the results where at least one of the fields matches the input map. (So a logical OR) however I would like it to return the logical AND of these fields.

Does anyone have suggestions on how to modify the existing code or a new way of efficiently querying the database?

Thank you

Answer 1

I don't know what this line is supposed to mean:

result[ ] = "$in"

As it is a compile-time error.

But the elements of the query document (the conditions) are in logical AND connection by default, so this is all it takes:

func sel(query map[string]string) bson.M {
    result := make(bson.M, len(query))
    for k, v := range query {
        result[k] = v
    }
    return result
}

If this gives you all the documents in the collection, then that means all the key-value pairs match all the documents. Experiment with simple filters to see that it works.

Also note that the mgo package also accepts a wide range of maps and structs, not just bson.M. Documentation of Collection.Find() has this to say about the allowed types:

The document may be a map or a struct value capable of being marshalled with bson. The map may be a generic one using interface{} for its key and/or values, such as bson.M, or it may be a properly typed map. Providing nil as the document is equivalent to providing an empty document such as bson.M{}.

So you can use your map which is of type map[string]string without converting it:

err = c.Find(items).Sort("-createdAt").All(&result)