3.0 API Migration guide

Please think of what the .NET developer needs to know most.

• .NET SDK Content: https://github.com/couchbase/docs-sdk-dotnet/blob/release/3.0/modules/project-docs/pages/migrating-sdk-code-to-3.n.adoc
• Common SDK content: https://github.com/couchbase/docs-sdk-common/blob/release/6.5/modules/shared/partials/migration.adoc
• What it looks like together (from Richard Smedley): https://docs.google.com/document/d/1S0oYzEsAEJnS2n1sgxSrzgg8h6CQPDCr6Q69cg1Ma3w/edit#

NOTES:

• See LCB migration guide for an example outline.
• Please add a warning about 6.5.0 prepared statement SDK incompatibility as well - DOC-6301