Override array settings in appsettings.json with those in appsettings.Production.json

Question

I'm using ASP.NET Core 2.1. I have settings in appsettings.json and I bind them to classes using the options pattern. I want to override some of them in appsettings.Production.json.

Overriding is supported according to the docs, and works for me generally. But it doesn't work for arrays.

appsettings.json:

"MySectionOuter": {   "MySectionInner": [     {       "foo": "1",       "bar": "2",       "baz": "3"     },     {       "foo": "a",       "bar": "b",       "baz": "c"     }   ] } 

My overrides in appsettings.Production.json

"MySectionOuter": {   "MySectionInner": [     {       "bar": "4",     },     {       "baz": "d"     }   ] } 

However that doesn't work - it adds rather than replaces.

I read that the array is syntactic sugar for a key-value store. So I also tried this:

"MySectionOuter": {   "MySection:1": {     "bar": "4",   },   "MySection:2": {     "baz": "b",   } } 

But that also doesn't work.

What is the correct syntax?

UPDATE

The comments show I haven't explained properly. What I want is like this:

During development:

element1: foo=1 element1: bar=2 element1: baz=3 element2: foo=a element2: bar=b element2: baz=c 

During production:

element1: foo=1 element1: bar=2 element1: baz=4  // this was changed element2: foo=a element2: bar=b element2: baz=d  // this was changed 

Answer 1

In fact, there are no arrays there when the configuration is built. It's just a key-value pair dictionary. So you end up with string keys, something like "mysectionouter:mysectioninner:0:foo" = 1.

So when in your config you define an array, the following happens:

appsettings.json:

"mysectionouter:mysectioninner:0:foo" = 1 "mysectionouter:mysectioninner:0:bar" = 2 

appsettings.production.json:

"mysectionouter:mysectioninner:0:bar" = new1 

result:

foo = 1 bar = new1 

So it's just index-based, and next configuration just overrides a key. In your second example, you achieve nothing but changing the index. Representation would be:

"mysectionouter:mysectioninner:1:bar" = new1 

So back to your question: arrays are tricky in appsettings, and though supported, are generally hard and not intuitive to use.

By index you may get a weird merge of two not related objects, if you define different sets of settings in your files, like settings A and B in the first config, and C in second, you will get C and B in the result, and you likely don't want to have B at all. Worse still, you can get a mix of A and C if you define only some fields of each object.

I'd recommend using some other files for storing this kind of information. You can also break in the debugger just where the configuration is loaded and see for yourself how these keys are build to get more insight.