How to create BSONDocument by passing it an array (rather than var args)

[sfte...@gmail.com]

Lets say I am create a BSONDocument like this right now:

BSONDocument(

"field1" -> "value1",

"field2" -> "value2"

)

That works.

But lets say I want to do this:

val fields = List(

"field1" -> "value1",

"field2" -> "value2"

)

BSONDocument(fields)

This does not work?  It will only save a field here if the value is of BSONValue type and no automatic conversions happen.  So that means you must manually use a BSONValue in your list like this: 

val fields = List(

"field1" -> BSONDateTime(new Date().getTime),

"field2" -> "value2"

)

BSONDocument(fields)

Here, field1 will get written, but field2 will not.

I have also tried unwrapping the list directly to the variable argument constructor like so:

BSONDocument(fields: _*)  

This does not work, complains that expects BSONElementSet but got List[String,Product with Serializable].  I would think it should be using implicit conversion here but isn't.... 

So what am I missing?  Why can't I simply move my variable argument list of Tuple2 into a List, and pass that list to the BSONDocument apply method?

[Cédric Chantepie]

Even w/o considering the goal of creating a document, the List is mis-typed (Product with Serializable).

[sfte...@gmail.com]

Ignore that - It doesn't matter what type I use for the list, it doesn't work regardless.  For example:

val fields : List[(String,Any)] = List(

"field1" -> "value1",

"field2" -> "value2"

)

BSONDocument(fields)

This will fail with "Type mismatch, expected: Seq[BSONElementSet], actual: List[(String,Any)]

The problem (as far as I can tell) is that while you CAN do this:

BSONDocument(

"field1" -> "value1",

"field2" -> "value2"

)

You CANT do this:

val fields : List[(String,Any)] = List(

"field1" -> "value1",

"field2" -> "value2"

)

BSONDocument(fields)

Because it would appear that the implicit conversion to a BSONValue is not happening?  Doing the latter will write nothing to the MongoDB, unless each of those values is specifically a BSONValue like BSONString("value1").  THEN it will write.

[Cédric Chantepie]

Having Any or Product as type means there is a mistyping issue. The specific type for each element being "erased" and unified to a meaningless type, compiler has no way to find the appropriate code instances for each value.

[Cédric Chantepie]

Similar to https://stackoverflow.com/questions/41446090/scala-no-json-serializer-found-for-type-any/41446446#41446446

[sfte...@gmail.com]

Do you have any suggestion as to how I can accomplish what I am after?

I want to be able to create a BSONDocument at runtime, with a variable number of parameters.  Ideally, this could be an list of Tuple2 objects, that I can pass to a BSONDocument() creator, like this:

val fields : List[(String,Any)] = List(

("field1","value1"),

("field2", 1234),

("field3", true)

)

BSONDocument(fields)

On Saturday, August 12, 2017 at 4:49:27 AM UTC-7, Cédric Chantepie wrote:

Similar to https://stackoverflow.com/questions/41446090/scala-no-json-serializer-found-for-type-any/41446446#41446446

[Cédric Chantepie]

As you should have read in the post for JSON, a list of JSON properties must be a list of (String, JsValue), and cannot be a list of (String, Any) (or a list of (String, Product)).

Similarly a list of BSON properties must be a list of (String, BSONValue).

[sfte...@gmail.com]

Clearly, I understand that it must be a Tuple[String,BSONValue]

But how can one do this:

BSONDocument(

"field1" -> "field2"

)

Here, as you can clearly see, "field2" is a String, not a BSONValue.  So, clearly, it is implicitly converted to a BSONValue.  

What I am after is the ability for this implicit conversion to be applied to a list.  Just as a BSONDocument can be created with any number of types like so:

BSONDocument(
"field1" -> "value1"   // String -> BSONString
"field2" -> 2  // Integer -> BSONInteger 

)

So too, I would like to be able to pass a list with these values which are then implicitly converted to BSONValues.  Is there just no way of doing this?

[sfte...@gmail.com]

Probably I am misunderstanding the implicit conversion.  When I think about it more, I do realize, that the compiler understands how to convert values in this case:

BSONDocument(

"field1":"value1"

)

Because the type of "value1" is known (String).  But a list of Any has no idea until runtime, what those values are, and so cannot implicitly convert them.

[Cédric Chantepie]

That's exactly why in such case of heterogenous values, the conversions must happen before being added added to the list, so that the types in this list are explicit unified in a meaningful way.