A hash expression is a map whose keys are DB column names which need to be filtered according
to the corresponding values. For example, HashExp{"level": 2, "dept": 10} will generate
the SQL: "level"=2 AND "dept"=10.
HashExp also handles nil values and slice values. For example, HashExp{"level": []interface{}{1, 2}, "dept": nil}
will generate: "level" IN (1, 2) AND "dept" IS NULL.
HashExp represents a hash expression.
A hash expression is a map whose keys are DB column names which need to be filtered according to the corresponding values. For example, HashExp{"level": 2, "dept": 10} will generate the SQL: "level"=2 AND "dept"=10.
HashExp also handles nil values and slice values. For example, HashExp{"level": []interface{}{1, 2}, "dept": nil} will generate: "level" IN (1, 2) AND "dept" IS NULL.