问题描述
我可以动态插入表列名问题是当我想在我的日志表中插入新值或旧值时,我得到一个字符串“old.Colname”或“new.Colname”而不是旧值或新值。
DECLARE C_USER VARCHAR(255);
DECLARE VARIABLE OPERATION_EVENT CHAR(8);
DECLARE GROUPIDNO INT;
DECLARE LOGDATAID_NO INT;
DECLARE VARIABLE FN CHAR(31);
DECLARE VARIABLE NEWCOL CHAR(31);
DECLARE VARIABLE OLDCOL CHAR(31);
BEGIN
SELECT CURRENT_USER FROM RDB$DATABASE INTO :C_USER;
IF (DELETING) THEN
BEGIN
OPERATION_EVENT = 'DELETE';
END
ELSE
BEGIN
IF (UPDATING) THEN
OPERATION_EVENT = 'UPDATE';
ELSE
OPERATION_EVENT = 'INSERT';
END
SELECT MAX(GROUPID) FROM LOG_DATA INTO :GROUPIDNO;
IF(GROUPIDNO IS NULL) THEN
GROUPIDNO = 1;
ELSE
GROUPIDNO = GROUPIDNO + 1;
IF(INSERTING) THEN
BEGIN
FOR SELECT RDB$FIELD_NAME FROM RDB$RELATION_FIELDS WHERE RDB$RELATION_NAME = 'araC' INTO :FN DO
BEGIN
OLDCOL = 'old.'||:FN;
NEWCOL = 'new.'||:FN;
INSERT INTO LOG_DATA (OLD_VALUE,NEW_VALUE,COLUMN_NAME,TABLE_NAME,OPERATION,CREATEDAT,USERS,GROUPID,LOGDATAID)
VALUES (:OLDCOL,:NEWCOL,:FN,'araC',trim(:OPERATION_EVENT),current_timestamp,:C_USER,:GROUPIDNO,:LOGDATAID_NO + 1);
END
END
这是我的日志表的屏幕截图,我想插入旧值和新值,但列名被插入为字符串
解决方法
问题是您试图将旧上下文和新上下文作为字符串引用,这是不可能的。具体问题是:
OLDCOL = 'old.'||:FN;
NEWCOL = 'new.'||:FN;
这会产生一个值为 'old.<whatever the value of FN is>'
的字符串(对于 new
也是如此)。它不会从 FN
或 OLD
上下文中生成名称在 NEW
中的列的值。
遗憾的是,无法按名称动态引用 OLD
和 NEW
上下文中的列。您将明确需要在代码中使用 OLD.columnname
和 NEW.columnname
,这意味着您需要编写(或生成)一个单独插入每一列的触发器。
或者,您可以升级到 Firebird 3,并使用 UDR 在本机代码、C# 或 Java(或其他支持的语言)中定义触发器。这些 UDR 引擎允许您动态引用旧上下文和新上下文中的列。
例如,使用 FB/Java external engine(查看存储库中关于如何安装 FB/Java 的自述文件):
创建一个 CHANGELOG
表:
create table changelog (
id bigint generated by default as identity constraint pk_changelog primary key,tablename varchar(31) character set unicode_fss not null,row_id varchar(30) character set utf8,columnname varchar(31) character set unicode_fss not null,new_value varchar(2000) character set utf8,old_value varchar(2000) character set utf8,operation char(6) character set ascii not null,modification_datetime timestamp default localtimestamp not null
)
还有一个 FB/Java 触发器:
package nl.lawinegevaar.fbjava.experiment;
import org.firebirdsql.fbjava.TriggerContext;
import org.firebirdsql.fbjava.Values;
import org.firebirdsql.fbjava.ValuesMetadata;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.EnumSet;
import java.util.Objects;
import java.util.Set;
import java.util.function.BiPredicate;
import static java.util.Collections.unmodifiableSet;
import static org.firebirdsql.fbjava.TriggerContext.Action.*;
public class ChangelogTrigger {
private static final Set<TriggerContext.Action> SUPPORTED_ACTIONS =
unmodifiableSet(EnumSet.of(INSERT,UPDATE,DELETE));
private static final int ROW_ID_LENGTH = 30;
private static final int VALUE_LENGTH = 2000;
private static final String INSERT_CHANGELOG =
"insert into changelog (tablename,row_id,columnname,new_value,old_value,operation) "
+ "values (?,?,?)";
public static void logChanges() throws SQLException {
TriggerContext ctx = TriggerContext.get();
TriggerContext.Action action = ctx.getAction();
if (!SUPPORTED_ACTIONS.contains(action)) {
return;
}
String tableName = ctx.getTableName();
if (tableName.equals("CHANGELOG")) {
throw new IllegalStateException("Cannot apply ChangelogTrigger to table " + tableName);
}
String identifierColumn = ctx.getNameInfo();
ValuesMetadata fieldsMetadata = ctx.getFieldsMetadata();
int identifierIdx = identifierColumn != null ? fieldsMetadata.getIndex(identifierColumn) : -1;
Values oldValues = ctx.getOldValues();
Values newValues = ctx.getNewValues();
Values primaryValueSet = action == INSERT ? newValues : oldValues;
String identifierValue = identifierIdx != -1
? truncate(asString(primaryValueSet.getObject(identifierIdx)),ROW_ID_LENGTH)
: null;
try (PreparedStatement pstmt = ctx.getConnection().prepareStatement(INSERT_CHANGELOG)) {
pstmt.setString(1,tableName);
pstmt.setString(2,identifierValue);
BiPredicate<Object,Object> logColumn = action == UPDATE
? ChangelogTrigger::acceptIfModified
: ChangelogTrigger::acceptAlways;
boolean batchUsed = false;
for (int idx = 1; idx <= fieldsMetadata.getParameterCount(); idx++) {
Object oldValue = oldValues != null ? oldValues.getObject(idx) : null;
Object newValue = newValues != null ? newValues.getObject(idx) : null;
if (logColumn.test(oldValue,newValue)) {
String columnName = fieldsMetadata.getName(idx);
pstmt.setString(3,columnName);
pstmt.setString(4,truncate(asString(newValue),VALUE_LENGTH));
pstmt.setString(5,truncate(asString(oldValue),VALUE_LENGTH));
pstmt.setString(6,action.name());
pstmt.addBatch();
batchUsed = true;
}
}
if (batchUsed) {
pstmt.executeBatch();
}
}
}
private static boolean acceptAlways(Object oldValue,Object newValue) {
return true;
}
private static boolean acceptIfModified(Object oldValue,Object newValue) {
return !Objects.equals(oldValue,newValue);
}
private static String asString(Object value) {
return value != null ? String.valueOf(value) : null;
}
private static String truncate(String value,int maxLength) {
if (value == null || value.length() <= maxLength) {
return value;
}
return value.substring(0,maxLength - 3) + "...";
}
}
这个 FB/Java 触发器非常通用,可以用于多个表。我还没有用所有数据类型测试过这个触发器。例如,要使触发器能够正确处理 blob 类型或其他二进制类型的列需要额外的工作。
使用 FB/Java 的 fbjava-deployer 实用程序构建触发器并将其加载到数据库中。
然后在你想要的表上定义触发器(在本例中,我在TEST_CHANGELOG
表上定义了它):
create trigger log_test_changelog
before insert or update or delete
on test_changelog
external name 'nl.lawinegevaar.fbjava.experiment.ChangelogTrigger.logChanges()!ID'
engine JAVA
外部名称定义了要调用的例程(nl.lawinegevaar.fbjava.experiment.ChangelogTrigger.logChanges()
)和表的(单个)主键列的名称(ID
),用于记录{{ {1}} 列。