ABP 7.0 JSON migration guide.

docs/en/Migration-Guides/Abp-7_0.md

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+# ABP Version 7.0 Migration Guide
+
+This document is a guide for upgrading ABP v6.0 solutions to ABP v7.0. There is a change in this version that may affect your applications, please read it carefully and apply the necessary changes to your application.
+
+## Hybrid JSON was removed.
+
+Since [System.Text.Json](https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/overview) library supports more custom features in NET 7, ABP no longer need the hybrid Json feature.
+
+### Previous Behavior
+
+There is a `Volo.Abp.Json` package which contains the `AbpJsonModule` module.
+`Serialization/deserialization` features of [System.Text.Json](https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/overview) and [Nettonsoft](https://www.newtonsoft.com/json/help/html/SerializingJSON.htm) are implemented in this module.
+
+We use [System.Text.Json](https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/overview) first,  More custom cases can be handled with [Nettonsoft](https://www.newtonsoft.com/json/help/html/SerializingJSON.htm) by configuring `UnsupportedTypes` of `AbpSystemTextJsonSerializerOptions`.
+
+### New Behavior
+
+We created `Volo.Abp.Json.SystemTextJson` and `Volo.Abp.Json.Newtonsoft` as separate packages, which means you can only use one of them in your project. The default is to use `SystemTextJson`. If you want `Newtonsoft`, please also use `Volo.Abp.AspNetCore.Mvc.NewtonsoftJson` in your web project.
+
+* Volo.Abp.Json.Abstractions 
+* Volo.Abp.Json.Newtonsoft
+* Volo.Abp.Json.SystemTextJson
+* Volo.Abp.Json (Depends on `Volo.Abp.Json.SystemTextJson` by default to prevent breaking)
+* Volo.Abp.AspNetCore.Mvc.NewtonsoftJson
+
+The `AbpJsonOptions` now has only two properties, which are
+
+* `InputDateTimeFormats(List<string>)`: Formats of input JSON date, Empty string means default format. You can provide multiple formats to parse the date.
+* `OutputDateTimeFormat(string)`: Format of output json date, Null or empty string means default format.
+
+Please remove all `UnsupportedTypes` add custom `Modifiers` to control serialization/deserialization behavior.
+
+Check the docs to see the more info: https://github.com/abpframework/abp/blob/dev/docs/en/JSON.md#configuration
+
+Check the docs to see how to customize a JSON contract: https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/custom-contracts
+