Simple approach to add objects in a many to many relationship

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I have 2 classes `ConfigurationCollection` and `OptionValues` which has a many to many relationship. I have tried solutions on the net to get it working. I tried adding another class to create two one to many relationship. But I am not understanding it the right way I suppose. And I also tried it without adding a third class.

Model classes

C#

public class ConfigurationCollection
{
    public int ConfigurationCollectionID { get; set; }
    public string CollectionName { get; set; }
    public int LsystemID { get; set; }

    public virtual Lsystem Lsystem { get; set; }
    public virtual ICollection<OptionValue> OptionValues { get; set; }
}
public class OptionValue
{
    public int OptionValueID { get; set; }
    public string OptionVal { get; set; }
    public int OptionID { get; set; }

    public virtual ICollection<ConfigurationCollection> ConfigurationCollections { get; set; }
    public virtual Option Option { get; set; }
}
public class Config_OptionVal
{
    public int Config_OptionValID { get; set; }
    public int OptionValueID { get; set; }
    public int ConfigurationCollectionID { get; set; }
    public bool OptionValChecked { get; set; }

    public virtual OptionValue OptionValue { get; set; }
    public virtual ConfigurationCollection ConfigurationCollection { get; set; }
}

Controller

C#

public ActionResult Create(int LsystemID)
{
    var model = new ConfigurationCollection
    {
      LsystemID = LsystemID,
      Lsystem = db.Lsystem.FirstOrDefault(x => x.LsystemID == LsystemID),
      OptionValues=new List<OptionValue>()
    };
    return View(model);
}

I am not sure what should be written in the Controller. I am able to populate the `OptionValues` in my View. I am just missing something that could save the data into the database.

Posted 4-Nov-15 23:14pm

vini vasundharan

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Nathan Minier · Answer 1 · 2015-11-05T01:28:00

In order to create a M->M relationship in entity Framework you'll need to use a mapping class, as you did with Config_OptionVal. Now it's important that that mapping class is the one that the classes on either side of the relationship operate through, you can't ignore that entity in the relationship. Therefore:

C#

public class ConfigurationCollection
{
    public int ConfigurationCollectionID { get; set; }
    public string CollectionName { get; set; }
    public int LsystemID { get; set; }
 
    public virtual Lsystem Lsystem { get; set; }
    public virtual ICollection<Config_OptionVal> Config_OptionVals{ get; set; }
}
public class OptionValue
{
    public int OptionValueID { get; set; }
    public string OptionVal { get; set; }
    public int OptionID { get; set; }
 
    public virtual ICollection<Config_OptionVal> Config_OptionVals{ get; set; }
    public virtual Option Option { get; set; }
}
public class Config_OptionVal
{
    public int Config_OptionValID { get; set; }
    public int OptionValueID { get; set; }
    public int ConfigurationCollectionID { get; set; }
    public bool OptionValChecked { get; set; }
 
    public virtual OptionValue OptionValue { get; set; }
    public virtual ConfigurationCollection ConfigurationCollection { get; set; }
}

Access across this relationship uses Config_OptionVal, like this:

C#

myContext.Set<config_optionval>().Where(x => x.OptionValueID == IDofInterest).ToArray();

myContext.Set<Config_OptionVal>().Where(x => x.ConfigurationCollectionID == IDofInterest).ToArray();

ConfigurationCollectionObject.Config_OptionVal.Select(x => x. OptionValue).ToArray();

OptionValueObject.Config_OptionVal.Select(x => x.ConfigurationCollection).ToArray();
</config_optionval>

So in your controller example, assuming LSystem and ConfigurationCollection are 1->1:

C#

public ActionResult Create(int LsystemID)
{
    var model = new ConfigurationCollection
    {
      LsystemID = LsystemID,
      Lsystem = db.Lsystem.FirstOrDefault(x => x.LsystemID == LsystemID),
      OptionValues= Lsystem != null 
          ? Lsystem.ConfigurationCollection.Config_OptionVal.Select(x => x.OptionValues).ToList() 
          : new List<optionvalue>();
    };
    return View(model);
}
</optionvalue>

And a couple of examples/tutorials:
MVC 5, Entity Framework 6 and Many to Many Relationship : a step by step View Model approach[^]

https://msdn.microsoft.com/en-us/library/dd742359.aspx[^]