I was surprised to learn that MongoDB can have multiple of the same key in the same document. So you might have a "map" that looks like this:
{"a": 1, "a": 2, "b": 3}
"a" maps to 2 different values in this case. Depending on how your languages driver works it's often difficult to see this is happening. In some languages you'll get "a" mapped to 1, and other languages will show "a" mapped to 2.
{"a": 1, "a": 2, "b": 3}
"a" maps to 2 different values in this case. Depending on how your languages driver works it's often difficult to see this is happening. In some languages you'll get "a" mapped to 1, and other languages will show "a" mapped to 2.