GitHub項目:jkrasnay/sqlbuilder的使用

http://www.jianshu.com/p/7f099b8cf5f0

技術選型:

在報表查詢時,一般須要作能夠動態添加的條件

在老項目中使用的是一種Tcondition的對象分裝sql

import java.util.HashMap;

public class TCondition {

    private String sql;

    private Object[] paraValues;

    private String orderBy;

    private String groupBy;

    private String having;

    /**
     * key爲表名,value爲 left join on後的內容(如何關聯的)
     */
    private HashMap<String,String> leftJoinMap;

    /**
     * count方法計數時可指定 count哪一個字段,默認爲count(1)
     */
    private String mainId;

    public TCondition() {

    }

    public TCondition(String sql, Object... paraValues) {
        this.setSql(sql);
        this.setParaValues(paraValues);
    }

    public static TCondition of() {
        return new TCondition();
    }

    public static TCondition of(String sql, Object... paraValues) {
        return new TCondition(sql, paraValues);
    }

    public String getSql() {
        return sql;
    }

    public TCondition setSql(String sql) {
        this.sql = sql;
        return this;
    }

    public Object[] getParaValues() {
        return paraValues;
    }

    public TCondition setParaValues(Object[] paraValues) {
        this.paraValues = paraValues;
        return this;
    }

    public String getOrderBy() {
        return orderBy;
    }

    public TCondition setOrderBy(String orderBy) {
        this.orderBy = orderBy;
        return this;
    }

    public String getGroupBy() {
        return groupBy;
    }

    public TCondition setGroupBy(String groupBy) {
        this.groupBy = groupBy;
        return this;
    }

    public String getHaving() {
        return having;
    }

    public TCondition setHaving(String having) {
        this.having = having;
        return this;
    }

    public String getMainId() {
        return mainId;
    }

    public TCondition setMainId(String mainId) {
        this.mainId = mainId;
        return this;
    }

    @Override
    public String toString() {
        StringBuffer result = new StringBuffer(this.getSql() + ":");
        for (int i = 0; i < paraValues.length; i++) {
            result.append(paraValues[i]).append(",");
        }
        result.append(" || ");
        return result.toString();
    }

    public HashMap<String, String> getLeftJoinMap() {
        return leftJoinMap;
    }

    public TCondition setLeftJoinMap(HashMap<String, String> leftJoinMap) {
        this.leftJoinMap = leftJoinMap;
        return this;
    }

可是因爲與老代碼的數據庫訪問層牢牢的耦合在一塊兒,沒法在另外的項目中進行復用,所以,在GitHub中找到了一款相似的封裝SQL查詢的對象

封裝的內容:

package ca.krasnay.sqlbuilder;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

/**
 * Tool for programmatically constructing SQL select statements. This class aims
 * to simplify the task of juggling commas and SQL keywords when building SQL
 * statements from scratch, but doesn't attempt to do much beyond that. Here are
 * some relatively complex examples:
 *
 * <pre>
 * String sql = new SelectBuilder()
 * .column("e.id")
 * .column("e.name as empname")
 * .column("d.name as deptname")
 * .column("e.salary")
 * .from(("Employee e")
 * .join("Department d on e.dept_id = d.id")
 * .where("e.salary > 100000")
 * .orderBy("e.salary desc")
 * .toString();
 * </pre>
 *
 * <pre>
 * String sql = new SelectBuilder()
 * .column("d.id")
 * .column("d.name")
 * .column("sum(e.salary) as total")
 * .from("Department d")
 * .join("Employee e on e.dept_id = d.id")
 * .groupBy("d.id")
 * .groupBy("d.name")
 * .having("total > 1000000").toString();
 * </pre>
 *
 * Note that the methods can be called in any order. This is handy when a base
 * class wants to create a simple query but allow subclasses to augment it.
 *
 * It's similar to the Squiggle SQL library
 * (http://code.google.com/p/squiggle-sql/), but makes fewer assumptions about
 * the internal structure of the SQL statement, which I think makes for simpler,
 * cleaner code. For example, in Squiggle you would write...
 *
 * <pre>
 * select.addCriteria(new MatchCriteria(orders, "status", MatchCriteria.EQUALS, "processed"));
 * </pre>
 *
 * With SelectBuilder, we assume you know how to write SQL expressions, so
 * instead you would write...
 *
 * <pre>
 * select.where("status = 'processed'");
 * </pre>
 *
 * To include parameters, it's highly recommended to use the
 * {@link ParameterizedPreparedStatementCreatorTest}, like this:
 *
 * <pre>
 * String sql = new SelectBuilder("Employee e")
 * .where("name like :name")
 * .toString();
 *
 * PreparedStatement ps = new ParameterizedPreparedStatementCreator(sql)
 * .setParameter("name", "Bob%")
 * .createPreparedStatement(conn);
 * </pre>
 *
 *
 * @author John Krasnay <john@krasnay.ca>
 */
public class SelectBuilder extends AbstractSqlBuilder implements Cloneable, Serializable {

    private static final long serialVersionUID = 1;

    private boolean distinct;

    private List<Object> columns = new ArrayList<Object>();

    private List<String> tables = new ArrayList<String>();

    private List<String> joins = new ArrayList<String>();

    private List<String> leftJoins = new ArrayList<String>();

    private List<String> wheres = new ArrayList<String>();

    private List<String> groupBys = new ArrayList<String>();

    private List<String> havings = new ArrayList<String>();

    private List<SelectBuilder> unions = new ArrayList<SelectBuilder>();

    private List<String> orderBys = new ArrayList<String>();

    private boolean forUpdate;

    private boolean noWait;

    public SelectBuilder() {

    }

    public SelectBuilder(String table) {
        tables.add(table);
    }

    /**
     * Copy constructor. Used by {@link #clone()}.
     *
     * @param other
     *            SelectBuilder being cloned.
     */
    protected SelectBuilder(SelectBuilder other) {

        this.distinct = other.distinct;
        this.forUpdate = other.forUpdate;
        this.noWait = other.noWait;

        for (Object column : other.columns) {
            if (column instanceof SubSelectBuilder) {
                this.columns.add(((SubSelectBuilder) column).clone());
            } else {
                this.columns.add(column);
            }
        }

        this.tables.addAll(other.tables);
        this.joins.addAll(other.joins);
        this.leftJoins.addAll(other.leftJoins);
        this.wheres.addAll(other.wheres);
        this.groupBys.addAll(other.groupBys);
        this.havings.addAll(other.havings);

        for (SelectBuilder sb : other.unions) {
            this.unions.add(sb.clone());
        }

        this.orderBys.addAll(other.orderBys);
    }

    /**
     * Alias for {@link #where(String)}.
     */
    public SelectBuilder and(String expr) {
        return where(expr);
    }

    public SelectBuilder column(String name) {
        columns.add(name);
        return this;
    }

    public SelectBuilder column(SubSelectBuilder subSelect) {
        columns.add(subSelect);
        return this;
    }

    public SelectBuilder column(String name, boolean groupBy) {
        columns.add(name);
        if (groupBy) {
            groupBys.add(name);
        }
        return this;
    }

    @Override
    public SelectBuilder clone() {
        return new SelectBuilder(this);
    }

    public SelectBuilder distinct() {
        this.distinct = true;
        return this;
    }

    public SelectBuilder forUpdate() {
        forUpdate = true;
        return this;
    }

    public SelectBuilder from(String table) {
        tables.add(table);
        return this;
    }

    public List<SelectBuilder> getUnions() {
        return unions;
    }

    public SelectBuilder groupBy(String expr) {
        groupBys.add(expr);
        return this;
    }

    public SelectBuilder having(String expr) {
        havings.add(expr);
        return this;
    }

    public SelectBuilder join(String join) {
        joins.add(join);
        return this;
    }

    public SelectBuilder leftJoin(String join) {
        leftJoins.add(join);
        return this;
    }

    public SelectBuilder noWait() {
        if (!forUpdate) {
            throw new RuntimeException("noWait without forUpdate cannot be called");
        }
        noWait = true;
        return this;
    }

    public SelectBuilder orderBy(String name) {
        orderBys.add(name);
        return this;
    }

    /**
     * Adds an ORDER BY item with a direction indicator.
     *
     * @param name
     *            Name of the column by which to sort.
     * @param ascending
     *            If true, specifies the direction "asc", otherwise, specifies
     *            the direction "desc".
     */
    public SelectBuilder orderBy(String name, boolean ascending) {
        if (ascending) {
            orderBys.add(name + " asc");
        } else {
            orderBys.add(name + " desc");
        }
        return this;
    }

    @Override
    public String toString() {

        StringBuilder sql = new StringBuilder("select ");

        if (distinct) {
            sql.append("distinct ");
        }

        if (columns.size() == 0) {
            sql.append("*");
        } else {
            appendList(sql, columns, "", ", ");
        }

        appendList(sql, tables, " from ", ", ");
        appendList(sql, joins, " join ", " join ");
        appendList(sql, leftJoins, " left join ", " left join ");
        appendList(sql, wheres, " where ", " and ");
        appendList(sql, groupBys, " group by ", ", ");
        appendList(sql, havings, " having ", " and ");
        appendList(sql, unions, " union ", " union ");
        appendList(sql, orderBys, " order by ", ", ");

        if (forUpdate) {
            sql.append(" for update");
            if (noWait) {
                sql.append(" nowait");
            }
        }

        return sql.toString();
    }

    /**
     * Adds a "union" select builder. The generated SQL will union this query
     * with the result of the main query. The provided builder must have the
     * same columns as the parent select builder and must not use "order by" or
     * "for update".
     */
    public SelectBuilder union(SelectBuilder unionBuilder) {
        unions.add(unionBuilder);
        return this;
    }

    public SelectBuilder where(String expr) {
        wheres.add(expr);
        return this;
    }
}

在後續的文章中我將介紹如何使用該組件,在報表項目中進行使 ^_^

github地址:

https://github.com/jkrasnay/sqlbuilder

博客:

http://john.krasnay.ca/2010/02/15/building-sql-in-java.html