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以findDTOByID为例。做一个说明例子，Forum为主表，Subject为Forum的字表，Post为Subject的字表。在Post里包含一个字段为Poster，指向Employee表。
类结果如下：AbstractTable定义Sql表的共同数据；表分为两种，一种是普通表class SQLTable extends AbstractTable，另一种是class JoinTable extends AbstractTable。还包括SQLField类，如下调用：
public String findByID(DTO dto) {
aliasIndex = 0;
SQLTable leaf = new SQLTable(dto, getFreeAlias());
leaf.where(dto.getPrimaryKey(), "=", "#{id}");
SQLTable cur = leaf;
for (JavaField jField : dto.getFields()) {
if (jField.getField().getType() instanceof ComponentType) {
DTO ref = (DTO) jField.getType();
SQLTable parent = new SQLTable(ref, getFreeAlias());
if (jField.getField().isNotNull()) {
JoinTable jtable = new JoinTable(JoinTable.Type.INNER, cur, leaf.findField(jField.getField().getJdbcName()), getFreeAlias());
parent.join(jtable);
}
else {
JoinTable jtable = new JoinTable(JoinTable.Type.LEFT, cur, leaf.findField(jField.getField().getJdbcName()), getFreeAlias());
parent.join(jtable);
}
cur = parent;
}
}
return cur.getSelectSQL();
}
其中DTO为一个表数据结构类，包含字段和类型等数据信息。
public class SQLTable extends AbstractTable {
public static final String SELECT = "SELECT ";
public static final String FROM = " FROM ";
public static final String WHERE = " WHERE";
public static final String ORDERBY = " ORDER BY";
public static final String LIMIT = " LIMIT ";
protected JoinTable join = null;
protected List<Where> wheres = new ArrayList<>();
protected List<OrderBy> orders = new ArrayList<>();
protected String limit;
public SQLTable(DTO dto, String tableAlias) {
super(dto.getName().toUpperCase(), tableAlias.toUpperCase());
fields = getSQLField(dto.getFields());
}
public JoinTable getJoinTable() {
return join;
}
public SQLTable join(JoinTable table) {
this.join = table;
return this;
}
public SQLTable where(JavaField field, String op, String val) {
SQLField sField = findField(field);
wheres.add(new Where(sField, op, val));
return this;
}
public SQLTable orderby(JavaField field, String order) {
SQLField sField = findField(field);
orders.add(new OrderBy(sField, order));
return this;
}
public SQLTable limit(String limit) {
this.limit = limit;
return this;
}
public SQLField getPrimaryKey() {
for (SQLField f : fields) {
if (f.isPrimaryKey()) {
return f;
}
}
return null;
}
public SQLField findField(String name) {
name = name.toUpperCase();
for (SQLField f : fields) {
if (f.getName().equals(name)) {
return f;
}
}
return null;
}
public SQLField findField(JavaField jField) {
for (SQLField f : fields) {
if (f.getJavaField() == jField) {
return f;
}
}
return null;
}
public String getSelectSQL() {
StringBuffer sb = new StringBuffer();
sb.append(SELECT);
sb.append(getSelectFieldsSQL());
if (join != null) {
sb.append(COMMA);
sb.append(join.getSelectFieldsSQL());
sb.append(FROM);
sb.append(" ( ");
sb.append(join.getChildTable().getSelectSQL());
sb.append(" ) ");
sb.append(join.getTableAlias());
sb.append(SPACE);
sb.append(join.getJoinSQL());
sb.append(SPACE);
sb.append(getTableName());
sb.append(SPACE);
sb.append(getTableAlias());
sb.append(" ON ");
sb.append(join.getTableAlias());
sb.append(DOT);
sb.append(join.findFieldByChildField().getName());
sb.append(" = ");
sb.append(getTableAlias());
sb.append(DOT);
sb.append(getPrimaryKey().getName());
}
else {
sb.append(FROM);
sb.append(getTableName());
sb.append(SPACE);
sb.append(getTableAlias());
if (wheres.isEmpty() == false) {
sb.append(WHERE);
for (Where w : wheres) {
sb.append(SPACE);
sb.append(getTableAlias());
sb.append(".");
sb.append(w.getField().getName());
sb.append(w.getOp());
sb.append(w.getVal());
}
}
if (orders.isEmpty() == false) {
sb.append(ORDERBY);
for (OrderBy orderby : orders) {
sb.append(SPACE);
sb.append(getTableAlias());
sb.append(".");
sb.append(orderby.getField().getName());
sb.append(SPACE);
sb.append(orderby.getOrder());
}
}
if (limit != null && limit.length() > 0) {
sb.append(LIMIT);
sb.append(limit);
}
}
return sb.toString();
}
private List<SQLField> getSQLField(List<JavaField> jFields) {
ArrayList<SQLField> fields = new ArrayList<>(jFields.size());
jFields.forEach(e-> {
String name = e.getField().getJdbcName();
SQLField f = new SQLField(e, this, name);
fields.add(f);
});
return fields;
}
}
下面是JoinTable
public class JoinTable extends AbstractTable {
protected Type type;
protected SQLTable childTable;
protected SQLField childKey;
public JoinTable(Type type, SQLTable childTable, SQLField childKey, String tableAlias) {
super(null, tableAlias.toUpperCase());
this.type = type;
this.childTable = childTable;
this.childKey = childKey;
for (SQLField field : getAllSQLFields()) {
SQLField f = new SQLField(this, field);
fields.add(f);
}
}
public SQLTable getChildTable() {
return childTable;
}
public SQLField getChildKey() {
return childKey;
}
public SQLField findFieldByChildField() {
SQLField p = childKey;
while (p!=null && p.getTable() != this) {
p = p.getUp();
}
return p;
}
public List<SQLField> getAllSQLFields() {
List<SQLField> fs = new ArrayList<>();
fs.addAll(childTable.getFields());
if (childTable.getJoinTable() != null) {
fs.addAll(childTable.getJoinTable().getFields());
}
return fs;
}
public String getJoinSQL() {
return type.name() + " JOIN";
}
public enum Type {
INNER, LEFT, RIGHT;
}
}
最后是SQLFIeld
public class SQLField {
private final JavaField jField;
private final String name;
private final AbstractTable table;
private SQLField up = null;
private SQLField down = null;
public SQLField(AbstractTable table, SQLField field) {
this(field.jField, table, field.getAlias());
this.down = field;
field.up = this;
}
public SQLField(JavaField jField, AbstractTable table, String name) {
this.jField = jField;
this.table = table;
this.name = name.toUpperCase();
}
public String getName() {
return name;
}
public String getAlias() {
return table.getTableAlias() +"_"+name;
}
public boolean isPrimaryKey() {
return jField.getField().getType() instanceof PrimaryKeyType;
}
public SQLField getUp() {
return up;
}
public SQLField getDown() {
return down;
}
public AbstractTable getTable() {
return table;
}
public JavaField getJavaField() {
return jField;
}
@Override
public String toString() {
return name;
}
运行后，生成的针对Post表的SQL查询ByID语句如下，其中换行是我手动添加的，原始是1行
SELECT D.EMPLOYEEID D_EMPLOYEEID,D.NAME D_NAME,
E.B_SUBJECTID E_B_SUBJECTID,E.B_FORUMID E_B_FORUMID,E.B_TITLE E_B_TITLE,E.B_CONTENT E_B_CONTENT,
E.C_A_POSTID E_C_A_POSTID,E.C_A_SUBJECTID E_C_A_SUBJECTID,E.C_A_POSTERID E_C_A_POSTERID FROM (
SELECT B.SUBJECTID B_SUBJECTID,B.FORUMID B_FORUMID,B.TITLE B_TITLE,B.CONTENT B_CONTENT,
C.A_POSTID C_A_POSTID,C.A_SUBJECTID C_A_SUBJECTID,C.A_POSTERID C_A_POSTERID FROM (
SELECT A.POSTID A_POSTID,A.SUBJECTID A_SUBJECTID,A.POSTERID A_POSTERID FROM POST A WHERE A.POSTID=#{id}
) C INNER JOIN SUBJECT B ON C.A_SUBJECTID = B.SUBJECTID
) E INNER JOIN EMPLOYEE D ON E.C_A_POSTERID = D.EMPLOYEEID三个表做内连接子查询，并自动为表和字段命名别名，再配合自动生成的mybatis的resultmap，可完成findbyid, findbypage, findbycount, insert, update, delete的生成。完整的生成mybatis xml文件
生成的类：
public class Post {
private Integer postID;
private Subject subject;
private Employee poster;
resultMap是
<resultMap type="net.xway.bbs.forum.dto.Post" id="POST">
<id property="PostID" column="C_A_POSTID"/>
<result property="subject.subjectID" column="B_SUBJECTID"/>
<result property="subject.forum" column="B_FORUMID"/>
<result property="subject.title" column="B_TITLE"/>
<result property="subject.content" column="B_CONTENT"/>
<result property="poster.employeeID" column="D_EMPLOYEEID"/>
<result property="poster.name" column="D_NAME"/>
</resultMap>