Database deleter (EF)

DatabaseDeleter.cs

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;

public class DatabaseDeleter
{
    static readonly string[] _ignoredTables =
    {
        "sysdiagrams",
        "usd_AppliedDatabaseScript",
        "__MigrationHistory"
    };

    readonly DbContext _dbContext;
    readonly Lazy<string> deleteSql;

    public DatabaseDeleter(DbContext dbContext)
    {
        _dbContext = dbContext;
        deleteSql = new Lazy<string>(GetDeleteSql);
    }

    string GetDeleteSql()
    {
        var allTables = GetAllTables();

        var allRelationships = GetRelationships();

        var tablesToDelete = BuildTableList(allTables, allRelationships);

        return BuildTableSql(tablesToDelete);
    }

    public virtual void DeleteAllObjects()
    {
        var sql = deleteSql.Value;

        _dbContext.Database.ExecuteSqlCommand(sql);
    }

    static string BuildTableSql(IEnumerable<string> tablesToDelete)
    {
        return tablesToDelete.Aggregate(string.Empty, (current, tableName) => current + string.Format("delete from [{0}];", tableName));
    }

    static string[] BuildTableList(ICollection<string> allTables, ICollection<Relationship> allRelationships)
    {
        var tablesToDelete = new List<string>();

        while (allTables.Any())
        {
            var leafTables = allTables.Except(allRelationships.Select(rel => rel.PrimaryKeyTable)).ToList();

            tablesToDelete.AddRange(leafTables);

            leafTables.ForEach(lt =>
            {
                allTables.Remove(lt);
                var relToRemove = allRelationships.Where(rel => rel.ForeignKeyTable == lt).ToList();
                relToRemove.ForEach(toRemove => allRelationships.Remove(toRemove));
            });
        }

        return tablesToDelete.ToArray();
    }

    IList<Relationship> GetRelationships()
    {
        const string sql =
            @"select
so_pk.name as PrimaryKeyTable
,   so_fk.name as ForeignKeyTable
from
sysforeignkeys sfk
	inner join sysobjects so_pk on sfk.rkeyid = so_pk.id
	inner join sysobjects so_fk on sfk.fkeyid = so_fk.id
order by
so_pk.name
,   so_fk.name";

        return _dbContext.Database.SqlQuery<Relationship>(sql).ToList();
    }

    IList<string> GetAllTables()
    {
        return _dbContext.Database.SqlQuery<string>("select name from sys.tables").Except(_ignoredTables).ToList();
    }

    class Relationship
    {
        public string ForeignKeyTable { get; set; }
        public string PrimaryKeyTable { get; set; }
    }
}