实体框架比较两个数据集

Question

I have a situation where I need to compare two sets of data from Sql Server. One set of data is held in a table (which is modelled in my Entity Framework model), however the other is the result set of a stored procedure. The fields returned by the stored procedure are identical to the fields in the table.

I had thought the following would work:

using (var db = new MyDatabaseContext()) {
    DbSet<MyTable> tableData = db.MyTables;
    DbSet<MyTable> procData = db.Set<MyTable>();
    procData.AddRange(db.MyTables.SqlQuery("exec dbo.MyProc").ToList();

    if (tableData.Count != procData.Count) return false;

    foreach (var data in tableData) {
        if (!data.Equals(procData.Find(data.ID))) return false;
    }
}

(side note: The MyTable class has been edited to implement IEquatable and override Equals so it's suitable for comparing at field level)

The logic being that I believed db.Set<MyTable> would create an arbitrary empty set of MyTable s which I could populate with the result of the stored procedure, and then compare that to the data in the table.

It appears I've misunderstood this, however, as checking the contents of tableData and procData at the first if line shows both contain exactly the same data (I've purposefully editted the stored procedure so it does not return the same data as in the table), leading me to believe that db.Set<Table> and db.MyTables both reference the same thing.

How can I achieve this?

Answer 1

db.MyTables has the same definition as what is returned in the line defining procData and initially contains the same objects.

(I assume your DbContext has the following, or something equivalent):

public DbSet<MyTable> MyTables { get; set; }

Calling db.Set<MyTable>() will give you a set equivalent to the property defined on the context.

If you are simply filtering in the stored procedure then tableData contains all records (so does procData ). When you attempt to add more records (which are ostensibly the same records contained in the set), EF will try and add the records with a state of "Added" . The thing is, your comparison isn't testing for the difference in state, and EF might not consider them added (if you configured your primary keys just so, EF might determine that the records already exist and state changes are unnecessary).