This post refers to the handling of array configuration items as they exist in ASP.Net core Configuration since 1.0 up to now (RT 2.0.5, SDK 2.1.4).

Example on how ASP.Net Core handles overwriting loaded array configuration when the later read config files contain less array entries than before.

Arrays are not complete replaced but only the first n entries that are actully given in the later config files are being replaced, leaving

There is an repository with a complete working example demonstrating the following behavior.

Example configuration files

appsettings.json

{
  "wizards": [
    {
      "Name": "Gandalf",
      "Age": "1000"
    },
    {
      "Name": "Harry",
      "Age": "17"
    }
  ]
}

appsettings2.json

{
  "wizards": [
    {
      "Name": "Houdini",
      "Age": "300"
    }
  ]
}

Setup

• read appsettings.json with two entries in ‘wizard’ array
• read additaonal appsettings2.json with only one array entry in ‘wizards’

Code

var builder = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json")
    .AddJsonFile("appsettings2.json");

(My) Expected output

the array is replaced by the latest definition resulting in only one entry in the array

    [wizards, ]
    [wizards:0, ]
    [wizards:0:Name, Houdini]
    [wizards:0:Age, 300]

Real Output

only the first entry of the existing array is overwritten, the second one remains

    [wizards, ]
    [wizards:1, ]
    [wizards:1:Name, Harry]
    [wizards:1:Age, 17]
    [wizards:0, ]
    [wizards:0:Name, Houdini]
    [wizards:0:Age, 300]

Issue

when having multiple sources of configuration items it’s somehwat unexpected behavior that the ultimate entries of an array depends on how many entries have been given in the setting sources before.

Expected behavor IMHO would be that the complete array would be replaced with the last set of entries.