I am writing a parser for one of website, which have products connected to categories. I am trying to build my own database with these items.
I have decided to use Entity Framework, but I am new to this framework, so here's my problem:
During parsing i have multiple items with same category. But categories are kind of trees. I mean, category have a reference to parentCategory.
During of parsing i have a list of category inheritance fe : category1 -> category1.1 -> category1.1.1
Each product I parse and add to database need to verify if that category exist and go through category inheritance to create non existing categories.
Code looks like this:
Category parentCategory = null;
foreach (var sCategory in categories)
{
var currentCategory = d.CategorySet.SingleOrDefault(category => category.Name == sCategory && category.Parent == parentCategory);
if (currentCategory == null)
{
currentCategory = new Category(){Name = sCategory,Parent = parentCategory};
if(parentCategory != null)
d.Entry(parentCategory).State = EntityState.Unchanged;
}
parentCategory = currentCategory;
}
But in this case, SingleOrDefault LinQ does not work because of exception:
Unable to create a constant value of type 'DataBaseModel.Category'. Only primitive types or enumeration types are supported in this context.
I know that I should compare IDs of category, but in this case it needs to saveChanges into db every time I add sth to DB.
Is there any other possibility to handle that?
I have solved this issue by creating local Dictionaries of Categories and before usage, fill this dictionaries by data from database.
_categoriesDictionary.Clear();
foreach (var category in this.Container.CategorySet)
{
Category temp = category;
string fullCategoryString = "";
while (temp != null)
{
fullCategoryString = fullCategoryString.Insert(0, temp.Name + ";");
temp = temp.Parent;
}
_categoriesDictionary.Add(fullCategoryString, category);
}
And then when analyzing the record:
Category parentCategory = null;
string fullCatString = "";
foreach (var sCategory in categories)
{
fullCatString += sCategory + ";";
Category currentCategory;
if (!_categoriesDictionary.TryGetValue(fullCatString, out currentCategory))
{
currentCategory = new Category()
{
Name = sCategory,
Parent = parentCategory
};
this.Container.CategorySet.Add(currentCategory);
_categoriesDictionary.Add(fullCatString, currentCategory);
}
parentCategory = currentCategory;
}
result.Category = parentCategory;
This has another adventage from my point of view: Its collecting data on start, and then do not query DB every time
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