在实体框架中为单个表手动创建模型

Question

Q1. How do I manually create a dead-simple entity framework model for a one-column table in my database, and query it?

The table looks like this:

CREATE TABLE dbo.MyTable (
    Value int NOT NULL CONSTRAINT PK_MyTable PRIMARY KEY CLUSTERED
);

And I have a POCO to map to it:

public class MyTable {
    public int Value { get; set; }
}

Q2. Then, how do I query MyTable with an Expression<Func<MyTable, bool>> lambda that will decide which rows to return and will get projected into the SQL?

I am relatively new to EF, but not to C# or software development. I'm asking this question because right now I just want to do a quick proof of concept of something in LINQPad, without using the EF Entity Data Model Wizard so it's easy to whip out code like this in the future.

Answer 1

All you need is in the code below, ready to be pasted to LinqPad

class MyTable
{
    public int Value { get; set; }
}

class MyTableConfiguration : EntityTypeConfiguration<MyTable>
{
    public MyTableConfiguration()
    {
        ToTable("dbo.MyTable");
        HasKey(x => x.Value);
        Property(x => x.Value).HasColumnName("Value").IsRequired();
    }
}

class MyDbContext : DbContext
{
    public IDbSet<MyTable> MyTableSet { get; set; }

    public MyDbContext(string connectionString) : base(connectionString)
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Configurations.Add(new MyTableConfiguration());
    }
}

void Main()
{
    MyDbContext context = new MyDbContext("Data Source=(local);Initial Catalog=SO33426289;Integrated Security=True;");
    Expression<Func<MyTable, bool>> expr = x => x.Value == 42;
    context.MyTableSet.Where(expr).Dump();
}

You need to make sure to reference EntityFramework NuGet package and System.ComponentModel.Annotations.dll . Here are the namespaces that I used:

System.ComponentModel.DataAnnotations.Schema
System.Data.Entity
System.Data.Entity.ModelConfiguration
System.Data.Entity.ModelConfiguration.Configuration

Answer 2

1. Either use EF's code first (eg data annonations) to define mappings and create a context class to access the entity set through or use an EDMX (model first or database first) for creating the models and the mappings and have the model and context generated for you. Search for any getting started with Entity Framework guide online.

Eg Code First (Search for Create the Data Model in this page) or for EDMX (Search for Creating the Entity Framework Data Model in this page).

2. Like so:

using (var context = new YourContext()) { var filteredEntities = context.YourEntities.Where(expression).ToList(); }

However, your table will need a PK (primary key) for this to work.