先说结论：属性名最好不加"_"，否则可能导致select返回值为null

如下是我做的测试：

1.属性名包含"_"

public class Manager {
    private Integer i_d;
    private String name;
    private Integer password;

    @Override
    public String toString() {
        return "Manager{" +
                "i_d=" + i_d +
                ", name='" + name + '\'' +
                ", password=" + password +
                '}';
    }

    public Integer getI_d() {
        return i_d;
    }

    public void setI_d(Integer i_d) {
        this.i_d = i_d;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getPassword() {
        return password;
    }

    public void setPassword(Integer password) {
        this.password = password;
    }
}

对应的manager表如下

测试结果如下

2.属性名不包含"_"

public class Manager {
    private Integer id;
    private String name;
    private Integer password;

    @Override
    public String toString() {
        return "Manager{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password=" + password +
                '}';
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getPassword() {
        return password;
    }

    public void setPassword(Integer password) {
        this.password = password;
    }
}

manager表如下：

测试结果如下