我的应用程序有以下模型结构。我有以下模型，
目前我正在开发另外两个模型（which are some how related with the above three models），即
我所做的是，i have to find a Attribute from a particular ProductGroup其中Attribute是ForeignKey模型中的FacetLines而ProductGroup ForeignKey中的FacetHeader Attribute 1}}。
提及 ProductGroup且ManyToMany与Product模型的关系也class FacetHeader(AbstractBaseModel):
"""
Defining the facets header that will be used during search.
"""
validators = [ChainIntegrityValidator, ScreenMethodValidator]
product_group = models.ForeignKey(
'products.ProductGroup',
help_text=_('The product group in which the facet header belongs'),
verbose_name=_('product group')
)
。
但这对我来说真的很难，因为我是Djang0的新人，我的模型结构对我来说有点复杂。所以，请看看我的模型结构，（这里我顺序代表我的模型）
FacetHeader
class FacetLines(AbstractBaseModel):
"""
Defining the facets lines that will be used during search.
"""
validators = [ChainIntegrityValidator, ScreenMethodValidator]
facet_header = models.ForeignKey(
'search.FacetHeader',
help_text=_('facet header to which facet lines belongs'),
verbose_name=_('facet header')
)
attribute = models.ForeignKey(
'products.Attribute',
help_text=_("attribute to which facet lines belongs"),
verbose_name=_("attribute"),
)
FacetLines
class Product(AbstractBaseModel):
"""
Describes product. products are basically parent product that does not
have a sku. For example, a product can be an Iphone 5, but the sku are the variants which
can be something like Iphone 5 Black, Iphone 5 Grey, etc.
"""
product_group = models.ManyToManyField(ProductGroup,
blank=True)
attributes = models.ManyToManyField(Attribute,
blank=True,
verbose_name=_("attributes"),
help_text=_('Select Attributes of product'),
through='ProductAttribute')
和产品
class ProductAttribute(AbstractAttribute):
"""
This is the through models that holds attribute value
for products
"""
validators = [ScreenMethodValidator, ChainIntegrityValidator]
product = models.ForeignKey(Product,
related_name='attribute_values',
verbose_name=_("Product"))
value_option = models.ManyToManyField(Option,
blank=True,
null=True,
verbose_name=_("Option"))
这是 ProductAttribute 模型
Attributes那么如何使用ProductGroup和FacetHeader模型获取特定FacetLines（即product_group_pk = 1）的所有FacetHeader。
更新
在这里，我使用内嵌表单集创建FacetLines多个FacetHeader，其中parent是FacetLines表单，when i select a particular product group from FacetHeader model是子表单。
我真正需要做的是，
FacetLines forms,there should be appear attribute of that selected product group of FacetHeader model然后在// This code is placed in the public domain
struct AllocatedMemory<'a> {
mem : &'a mut [u8],
next : Option<&'a mut AllocatedMemory <'a> >,
}
struct Alloc<'a> {
glob : Option<&'a mut AllocatedMemory <'a> >,
}
impl<'a> Alloc <'a> {
fn alloc_cell(self : &mut Alloc<'a>) -> &'a mut AllocatedMemory<'a> {
match self.glob {
Some(ref mut glob_next) => {
let rest : Option<&'a mut AllocatedMemory <'a> >;
match glob_next.next {
Some(ref mut root_cell) => {
rest = std::mem::replace(&mut root_cell.next, None);
},
None => rest = None,
}
match std::mem::replace(&mut glob_next.next, rest) {
Some(mut root_cell) =>
{
return root_cell;
},
None => panic!("OOM"),
}
},
None => panic!("Allocator not initialized"),
}
}
fn free_cell(self : &mut Alloc<'a>,
mut val : & 'a mut AllocatedMemory<'a>) {
match self.glob {
Some(ref mut glob_next) => {
match std::mem::replace(&mut glob_next.next ,None) {
Some(mut x) => {
let _discard = std::mem::replace(&mut val.next, Some(x));
},
None => {},
}
glob_next.next = Some(val);
},
None => panic!("Allocator not initialized"),
}
}
}
struct AllocatorGlobalState<'a>{
cell1 : AllocatedMemory<'a>,
cell0 : AllocatedMemory<'a>,
sentinel : AllocatedMemory<'a>,
allocator :Alloc<'a>,
}
fn main() {
let mut buffer0 : [u8; 1024] = [0; 1024];
let mut buffer1 : [u8; 1024] = [0; 1024];
let mut sentinel_buffer : [u8; 1] = [0];
let mut ags : AllocatorGlobalState = AllocatorGlobalState {
cell1 : AllocatedMemory{mem: &mut buffer1[0..1024],
next: None},
cell0 : AllocatedMemory{mem: &mut buffer0[0..1024],
next: None},
sentinel : AllocatedMemory{mem: &mut sentinel_buffer[0..1], next: None},
allocator : Alloc {glob : None},
};
ags.allocator.glob = Some(&mut ags.sentinel);
ags.allocator.free_cell(&mut ags.cell1);
ags.allocator.free_cell(&mut ags.cell0);
{
let mut x = ags.allocator.alloc_cell();
x.mem[0] = 4;
let mut y = ags.allocator.alloc_cell();
y.mem[0] = 4;
ags.allocator.free_cell(y);
let mut z = ags.allocator.alloc_cell();
z.mem[0] = 8;
//y.mem[0] = 5; // <-- this is an error (use after free)
}
}
。