feat: TypeHandler support - #162
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| // Example using a module-level attribute | ||
| using Dapper; | ||
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| [module: TypeHandler<YourDotNetType, YourCustomTypeHandler>] |
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If I have a query that required certain set of typeHandlers,
And other do not,
Then how to restore them, and then add if and when needed ?
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Hello, this PR does not currently allow for switching or disabling type handlers on the fly.
This is definitely a feature that could be added, though.
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Any update on this PR or #117? I am debugging custom Dapper.AOT I have registered them via and they are not used in source generation and I just get runtime cast errors when loading data from DB "Invalid cast from 'System.Int64' to 'MyCustomType'." What is the purpose of |
mgravell
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Aug 23, 2026
SqlMapper.AddTypeHandler registrations now work under interception, in both directions, by delegating to vanilla's own decision procedure at execution time rather than trying to see runtime state at compile time: - writes: a member type the generator does not recognize emits a dispatch through SqlMapper.LookupDbType (public, CS0618-suppressible - the same tier as PackListParameters): handler present -> handler.SetValue (with DBNull for null, never null itself - the TypeHandler<T> interface impl NREs on a raw null); otherwise any returned DbType is applied and the value binds raw as before (demand:false deliberately - modern providers natively handle types vanilla's map does not, DateOnly being the live case until the Dapper re-enable ships). Update-mode mirrors it, so command reuse stays legal (the parameter shape is stable); an expandable member checks the handler *first*, which is the order vanilla applies (a handled collection type must not list-expand - Issue253). - reads: the lib cannot reference Dapper (a consumer may use Dapper or Dapper.StrongName, and a hard reference would split the handler registry between the two), so generated code installs a TypeHandlerBridge from a module initializer, compiled against the consumer's own Dapper; the flexible read path consults it, and a whole-type handler overrides a generated row factory (RowFactory<T>.Resolve), matching vanilla's handler-before-member-binding order. A ModuleInitializerAttribute polyfill is emitted for down-level targets, probe-gated like the interceptor attribute; the whole feature is inert against a Dapper too old to have HasTypeHandler/LookupDbType. - char/char? stay excluded (their StringFixedLength map entry pads the round-trip); object/dynamic stay excluded (runtime-typed values); ParamMember gains TypeOfName, mirroring RowMember's, because typeof on an annotated reference type or dynamic does not compile. This also clears the bare-DataTable TVP shape and the Xml types for free - vanilla registers DataTableHandler and the XML handlers by default, and the dispatch reaches them like any other registration. Dapper test suite: 677 -> 705/793. Design and probed facts in notes/typehandlers-design.md; prior art PRs #117 and #162 (the announced- attribute tier) remain as the static-dispatch optimization, redone on the plain-data model.
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This PR represents an attempt to resolve issue #159.
The prior approach of the source generator (#117) inadvertently led to the generation of code that instantiated a new
TypeHandlerobject for each parameter or column read operation (new global::CustomClassTypeHandler().Read(...)). This could lead to unnecessary object allocations and a minor performance overhead, especially in high-volume scenarios.This PR introduces a
TypeHandlerInstanceRegistryand modifies the code generation to ensure that:__Handler1,__Handler2).