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IEvangelist merged 2 commits into from
Nov 8, 2021
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JSON number handling breaking change #26848

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json number handling
gewarren Nov 6, 2021
ab474ec
remove xref
gewarren Nov 6, 2021
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1 change: 1 addition & 0 deletions docs/core/compatibility/6.0.md
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Expand Up @@ -131,6 +131,7 @@ If you're migrating an app to .NET 6, the breaking changes listed here might aff
| [IAsyncEnumerable serialization](serialization/6.0/iasyncenumerable-serialization.md) | ✔️ | ❌ | Preview 4 |
| [JSON source-generation API refactoring](serialization/6.0/json-source-gen-api-refactor.md) | ❌ | ✔️ | RC 2 |
| [JsonNode no longer supports C# `dynamic` type](serialization/6.0/jsonnode-dynamic-type.md) | ❌ | ✔️ | Preview 7 |
| [JsonNumberHandlingAttribute on collection properties](serialization/6.0/jsonnumberhandlingattribute-behavior.md) | ❌ | ✔️ | RC 1 |
| [New JsonSerializer source generator overloads](serialization/6.0/jsonserializer-source-generator-overloads.md) | ❌ | ✔️ | Preview 6 |

## Windows Forms
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46 changes: 46 additions & 0 deletions docs/core/compatibility/serialization/6.0/jsonnumberhandlingattribute-behavior.md
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---
title: "Breaking change: JsonNumberHandlingAttribute on non-number collection properties"
description: Learn about the .NET 6 breaking change where JsonNumberHandlingAttribute can now only be applied to properties that are collections of numbers.
ms.date: 11/05/2021
---
# JsonNumberHandlingAttribute on collection properties

A minor breaking change was introduced in .NET 6 with regard to the <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> attribute. If you apply the attribute to a property that's a collection of non-number values and attempt to serialize or deserialize the property, an <xref:System.InvalidOperationException> is thrown. The attribute is only valid for properties that are collections of number types, for example:

@IEvangelist IEvangelist Nov 8, 2021

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Suggested change
A minor breaking change was introduced in .NET 6 with regard to the <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> attribute. If you apply the attribute to a property that's a collection of non-number values and attempt to serialize or deserialize the property, an <xref:System.InvalidOperationException> is thrown. The attribute is only valid for properties that are collections of number types, for example:
A breaking change was introduced in .NET 6 with regard to the <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> attribute. If you apply the attribute to a property that's a collection of non-number values and attempt to serialize or deserialize the property, an <xref:System.InvalidOperationException> is thrown. The attribute is only valid for properties that are collections of number types, for example:

I'm not sure it's a good idea to classify this as a "minor" breaking change. Any one who had code in place before that used this attribute in this way, would now experience an exception. It's still a breaking change, even though it may not affect as many consumers.


```csharp
[JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
public List<int> MyList { get; set; }
```

## Previous behavior

Although it was ignored during serialization, <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> could be applied to properties that were collections of non-number types. For example:

```csharp
[JsonNumberHandling(JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.WriteAsString)]
public List<MyClass> MyList { get; set; }
```

## New behavior

Starting in .NET 6, if you apply <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> to a property that's a collection of non-number values and attempt to serialize or deserialize the property, an <xref:System.InvalidOperationException> is thrown.

## Version introduced

6.0 Preview 1

## Type of breaking change

This change can affect [binary compatibility](../../categories.md#binary-compatibility).

## Reason for change

This change was a side effect of a performance optimization for the number handling feature.

## Recommended action

Remove the <xref:System.Text.Json.Serialization.JsonNumberHandlingAttribute> attribute from incompatible collection properties.

## Affected APIs

All of the <xref:System.Text.Json.JsonSerializer?displayProperty=fullName> serialization and deserialization methods.
4 changes: 4 additions & 0 deletions docs/core/compatibility/toc.yml
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href: serialization/6.0/json-source-gen-api-refactor.md
- name: JsonNode no longer supports C# `dynamic`
href: serialization/6.0/jsonnode-dynamic-type.md
- name: JsonNumberHandlingAttribute on collection properties
href: serialization/6.0/jsonnumberhandlingattribute-behavior.md
- name: New JsonSerializer source generator overloads
href: serialization/6.0/jsonserializer-source-generator-overloads.md
- name: Windows Forms
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href: serialization/6.0/json-source-gen-api-refactor.md
- name: JsonNode no longer supports C# `dynamic`
href: serialization/6.0/jsonnode-dynamic-type.md
- name: JsonNumberHandlingAttribute on collection properties
href: serialization/6.0/jsonnumberhandlingattribute-behavior.md
- name: New JsonSerializer source generator overloads
href: serialization/6.0/jsonserializer-source-generator-overloads.md
- name: .NET 5
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