fix(database/gdb): handle empty string in Fields() gracefully

[lingcoder]

Summary

Fix bug where Fields("") with empty string generates invalid SQL SELECT FROM table.

Root Cause

mappingAndFilterToTableFields method doesn't skip empty strings when processing fields:

• gstr.SplitAndTrim("", ",") returns empty array
• No fields added to query
• Results in invalid SQL: SELECT FROM table

Fix

Skip empty string fields in mappingAndFilterToTableFields (line 97-100):

// Skip empty string fields
if fieldStr == "" {
    continue
}

Behavior Changes

• Fields("") → SELECT * FROM table (uses default)
• Fields("", "id") → SELECT id FROM table (ignores empty string)
• Fields("id", "", "nickname") → SELECT id, nickname FROM table

Tests

Added Test_Issue4697 with 3 scenarios covering all cases above.

Related

Fixes #4697
Ref #4703 (discovered during pagination test development)

[Copilot]

Pull request overview

Fixes a gdb.Model.Fields("") edge case that could lead to generating invalid SQL (SELECT FROM table) by ignoring empty-string field inputs so the query falls back to the default field selection.

Changes:

• Skip empty-string field entries during field mapping/filtering in mappingAndFilterToTableFields.
• Add a MySQL driver regression test covering Fields("") and mixed empty/non-empty field inputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
database/gdb/gdb_model_utility.go	Ignores empty-string field tokens during field mapping to prevent empty select lists.
contrib/drivers/mysql/mysql_z_unit_issue_test.go	Adds regression coverage for issue #4697 (empty-string fields).

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[lingcoder]

已调整