如何将数据从ModelForm保存到django中的数据库？

我有一个模型：

class Cost(models.Model):
    project = models.ForeignKey(Project)
    cost = models.FloatField()
    date = models.DateField()

对于模型，我创建了一个 ModelForm 类：

For the model I created a ModelForm class:

class CostForm(ModelForm):
    class Meta:
        model = Cost
        fields = ['date', 'cost']

与 view.py ：

def cost(request, offset):
    if request.method == 'POST':
        # NOTE: How to save the data in DB?
        return HttpResponseRedirect('/')
    else:
        form = CostForm()

和下一个模板：

<form action="/cost/{{ project }}/" method="post" accept-charset="utf-8">
    <label for="date">Date:</label><input type="text" name="date" value={{ current_date }} id="date" />
    <label for="cost">Cost:</label><input type="text" name="cost" value="0" id="cost" />
    <p><input type="submit" value="Add"></p>
</form>

问题

可以将数据从表单保存到数据库中？

model.py 包含

class Project(models.Model):
    title = models.CharField(max_length=150)
    url = models.URLField()
    manager = models.ForeignKey(User)
    timestamp = models.DateTimeField()

我的尝试

我试图在一个下一个方法（注意：offset =项目名称）：

My attempt

I tried to implement the solution in a next way (note: offset = project name):

def cost(request, offset):
    if request.method == 'POST':
        form = CostForm(request.POST)
        if form.is_valid():
            instance = form.save(commit=False)
            instance.project = Project.objects.filter(title=offset)
            instance.date = request.date
            instance.cost = request.cost
            instance.save()
        return HttpResponseRedirect('/')
    else:
        form = CostForm()

但它不起作用：（