custom type mapping implementation#2866
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Summary
Custom mapping is part of JDBC responsibility. Client provides rich API to get values in different forms. If more custom conversion is needed it is part of external work and application responsibility.
JDBC is the layer that used for its portability and conversion in its case is main job it does.
The problem mainly relate to CH types that hardly can be mapped to Java conterpart. For example,
UInt64doesn't fitlongso it can be returned asBigIntegeror asString. By default, JDBC driverreturns
BigIntegerbut user want to getStringinstead. What is completely valid case. In the JDBC context it means that columns that haveUInt64like types should be presented as if they areStringcolumns. There are two parts of support: one is what
ResultSet#getObject()returns and another isResultSetMetadatathat describes structure of result set. The last one must returnStringtypefor such columns.
Custom mapping implementation is complex because of many different classes involved. It requires extensive testing and some preparation. Here are overall steps needed for implementation.
Today we need to add next conversion to
java.lang.Stringfor types:UInt64,UInt128,Int128,UInt256,Int256,Float32,Float64,BFloat16,Decimal,Decimal32,Decimal64,Decimal128,Decimal256.It means columns with only this base types can be converted to
String. NoDynamic, noVariant, no nested types would work that way. This should be clearly documented.Closes
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Medium Risk
Touches core result-set type binding and connection configuration; mis-mapped types could cause runtime conversion errors, but behavior is opt-in via driver properties and covered by new integration tests.
Overview
Adds configurable JDBC type mappings so ClickHouse column types (e.g.
UInt64) can be read as a chosen Java type such asString, with metadata andgetObject()staying aligned.Configuration: New driver properties
jdbc_type_mappings(and deprecatedtypeMappings) accept comma-separatedClickHouseType=JavaClasspairs via URL orProperties.JdbcConfigurationparses them into an immutable map (with common class name shortcuts andClass.forNamefallback); specifying both property names fails at connect time.Connection API:
Connection#getTypeMap/setTypeMapare implemented (replacing unsupported stubs). The connection keeps an immutable type map snapshot; result sets capture it at open so concurrentsetTypeMapdoes not change binding mid-iteration.Binding logic: Column class/JDBC type resolution moves into
ResultSetMetaDataImpl(per-column bindings +resolveColumnClass).ResultSetImpland prepared-statement metadata pass the connection type map so overrides affectgetColumnClassName,getColumnType, andgetObject(including pre-execute prepared metadata from query schema).JdbcUtilsaddsCLASS_TO_SQL_TYPE_MAPso overridden Java classes map back to a sensible JDBC type.Minor:
ClientUtilsgainsisBlank/ refactorsisNotBlank. Integration tests cover URL/properties parsing, connection type map, metadata, and result materialization.Reviewed by Cursor Bugbot for commit 0fdaafa. Bugbot is set up for automated code reviews on this repo. Configure here.