web2py中的级联/依赖下拉列表

Question

我在尝试在web2py中创建级联下拉列表时遇到一些问题。我遵循了这个方法，然而，我（一个初学者）很难理解它背后的逻辑。

http://www.web2pyslices.com/slice/show/1526/cascading-drop-down-lists-with-ajax-2

我已经设法稍微适应它，但我在尝试向级联/序列中添加更多表时遇到了麻烦

所以目前我有下面的代码，我想要做的是从“tax_class”表中返回一个值列表，根据“tax_phylum”表中的选择结果

模型

db.define_table('tax_kingdom',
                Field('name'))

db.define_table('tax_phylum',
                Field('name', 'string'),
                Field('kingdom_id'))
db.tax_phylum.kingdom_id.requires = IS_IN_DB(db, db.tax_kingdom.id, '%(name)s')

db.define_table('tax_class',
                Field('name', 'string'),
                Field('phylum_id'))
db.tax_class.phylum_id.requires = IS_IN_DB(db, db.tax_phylum.id, '%(name)s')

控制器

def index():
    kingdoms = db().select(db.tax_kingdom.ALL)

    if request.vars.kingdom_name:
        phylum_select = db(db.tax_phylum.id == request.vars.kingdom_name).select(db.tax_phylum.ALL)
    else:
        phylum_select = db(db.tax_phylum.id == 1).select(db.tax_phylum.ALL)
    return dict(kingdoms=kingdoms, phylum_select=phylum_select)


def phylum():
    phylums = db(db.tax_phylum.kingdom_id == request.vars.kingdom_name).select(db.tax_phylum.ALL)
    result = ""
    for p in phylums:
        result += "<option value='" + str(p.id) + "'>" + p.name + "</option>"
    return XML(result)

视图

{{extend 'layout.html'}}

<form enctype="multipart/form-data" action="{{URL()}}" method="post">
    <select name='kingdom_name'
        onchange="jQuery('#kingdom_name').empty();
        ajax('phylum', ['kingdom_name'], 'phylum_name');">
        {{for kingdom in kingdoms:}}
            <option value="{{=kingdom.id}}"
                {{=" selected='selected'" if str(kingdom.id)==request.vars.kingdom_name else ""}}>
            {{=kingdom.name}}
            </option>
        {{pass}}
    </select>


<select id='phylum_name' name='phylum_name' >
    <!-- loop through the index function i -->
        {{for phylum in phylum_select:}}
            <option value="{{=phylum.id}}"
                {{=XML(" selected='selected'") if str(phylum.id)==request.vars.phylum_name else ""}}>
            {{=phylum.name}}</option>
        {{pass}}
    </select>


</form>