使用LINQ to SQL基于密钥连接两个表

Question

I've got Two tables Attribute(AID, Name, Description) AttributeVal(AID,Value)

Now, Using LINQ I need to get the Name, Description and Value by joining these two tables. So, far I got here..

        var displayAttributeMap = dctx.Attributes.Join(dctx.AttributeDisplayNames, a => a.AttributeID, adn => adn.AttributeID, 
                                                        (a, adn) => new
                                                        {
                                                            AttributeName = a.Name,
                                                            AttributeDispName = adn.DisplayName
                                                        }
                                                       ).ToDictionary(a => a.AttributeName, a => a.AttributeDispName);

But here I don't know where to insert a condition on the foreign key, in my case it is Attribute ID. Am I missing something here or should I use LINQ directly?

Answer 1

From what I gather, you need the value AND the display name of the attribute put into a dictionary.

All you need to do is add another join to your current query and change your select and ToDictionary around a bit. I find using the query syntax easier to read and use when dealing with joins.

(from attr in dctx.Attributes
    join attrDisplayName in dctx.AttributeDisplayNames on attr.AttributeID equals attrDisplayName.AttributeID
    join attrVal in dctx.AttributeVal on attr.AttributeID equals attrVal.AttributeID
select new
{
    AttributeName = attr.Name,
    AttributeDispName = attrDisplayName.DisplayName,
    AttributeID = attr.AttributeID,
    AttributeValue = attrVal.Value
}).ToDictionary(key => key.AttributeID, (value) => { return new { DisplayName = value.AttributeDispName, Value = value.AttributeValue };})

I haven't tested it but LinqPad is happy with the syntax, so I think it should work.