C#查询基于外键获取行

Question

I have two tables:

Component

and Component Profile

ComponentId is a foreign key to Component Profile

What I want to do is fetch All Component for a specific Business entity Id and then display all component Profiles for those Component ids from C#

I have been able to retrieve all components for a given business entity id

var component = context.Components.Where(i => i.BusinessEntityId == businessEntityId ).ToList();

I want to retrieve distinct component ids so that I can get all Component Profiles from it. How do i achieve this, Component Id is unique for each Profile. I am hoping that once I get distinct component Ids

foreach (var componentObject in componentObjects)
{
    var componentId = componentObject.Id;
    var componentProfile= context.ComponentProfiles.Where(i => i.ComponentId.Value == componentId);

    if (componentProfile != null)
    {
        result.Add(componentProfile.Map<Libraries.Entities.ComponentProfile>());
    }
}
               

What is an easy way to do this?

Answer 1

If I understand your question correctly, you can use Include .

var components = context.Components
     .Include("ComponentsProfiles") // I believe it is plural, but you need to check.
     .Where(i => i.BusinessEntityId == businessEntityId )
     .ToList();

You then loop through components, and get the corresponding component profiles.

foreach(var component in components) {
   var componentProfiles = component.ComponentsProfiles;
}

FYI: It is better to have unique identifier column in ComponentProfile table.

Answer 2

I renamed your initial variable to be plural, since it returns multiple rows:

var components = context.Components.Where(i => i.BusinessEntityId == businessEntityId).ToList();

Now you can group your components by ComponentId so they are distinct:

var componentGroups = components.GroupBy(c => c.ComponentId);

Now you can combine the components that have each ComponentId with the ComponentProfile :

var componentProfiles = componentGroups.Select(cg => new { Components = cg.Select(c => c), Profile = context.ComponentProfiles.Single(cp => cp.ComponentId == cg.Key) });

So componentProfiles is an anonymous object that combines the list of Components rows with what I enforced is the single ComponentProfiles row that they use.

Answer 3

This solution combines all the code into a single Linq query.

var context = GetCoreDbEntityContext(businessEntityId);
var result = context.Components
    .Where(i => i.BusinessEntityId == businessEntityId)    // find relevant components
    .Select(c => new { c.ComponentId, c.BusinessEntityId })    // isolate the fields needed
    .Distinct()    // find distinct combinations of fields
    .Join(    // inner join distinct combinations with ComponentProfiles
        context.ComponentProfiles,    // table or list to inner join with
        c => c.ComponentId,    // key selector from Components used in join
        p => p.ComponentId,    // key selector from ComponentProfiles used in join
        (c, p) => new {    // select individual fields or table(s) as needed
            c.BusinessEntityId,    // individual component business entity ID
            c,    // all Component fields
            p    // all ComponentProfile fields
        })
    .Select(r => r.p)    // (optional) reduce columns to only ComponentProfiles
    .ToList();

return result;    // contains list of ComponentProfiles

Alternatively, if you only need the componentProfiles, you could do this.

var context = GetCoreDbEntityContext(businessEntityId);
var result = context.ComponentProfiles
    .Where(p => context.Components
        .Where(i => i.BusinessEntityId == businessEntityId)    // find relevant components
        .Any(c => c.ComponentId == p.ComponentId)    // include rows with matching ComponentId
    ).ToList();

return result;    // contains list of ComponentProfiles

Answer 4

This seemed to work out from all the pieces answered:

 try
        {
            var context = GetCoreDbEntityContext(businessEntityId);
            var components = context.Components.Where(i => i.BusinessEntityId == businessEntityId).ToList();
            var componentIdsDistinct = components.Select(c => c.Id).Distinct();

            foreach (var componentId in componentIdsDistinct)
            {
                var componentProfile = context.ComponentProfiles.SingleOrDefault(i => i.ComponentId == componentId);
                if (componentProfile != null)
                {
                    result.Add(componentProfile.Map<Libraries.Entities.ComponentProfile>());
                }
            }
            return result;
        }

Answer 5

There is a one-to-many relation between Profiles and Components :

• Every Component has exactly one Profile (using a foreign key with a rather confusing name. I'll use ProfileId );
• Every Profile may be used by zero or more Components .

Because one Profile may be used by several Components , there may be several 'Components' with the same foreign key value 'ProfileId`

I want to fetch All Component for a specific Business entity Id and then display all component Profiles for those Component ids

So given a businessEntityId , you need to find all Components with this businessEntityId . Once you've got these components, you can find the Profiles that belong to these components. As said, several Components may belong to the same Profile , so you'll have to use Distinct to remove duplicates.

var result = MyComponents
    // keep only the components with businessEntityId
    .Where(component => component.BusinessEntityId == businessEntitId)
    .Join(MyProfiles,                      // Join with Profiles
        component => component.ProfileId,  // from every component take the foreign key
        profile => profile.Id,             // from every profile take the primary key
        (component, profile) =>            // when they match
            profile)                       // keep the matching profile
    .Distinct()                            // and remove duplicates