基于模型生成mybatis xml中sql语句



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 wheres = new ArrayList<>();
	protected List 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 getSQLField(List jFields) {
		ArrayList 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 getAllSQLFields() {
		List 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