LinqDB 查询数据库

LinqDB数据库查询数据，还是很方便的。

1. 添加Entity数据实体类

方便之后映射操作

     /// <summary>
     /// 课件
     /// </summary>
     [DataContract]
     [Table("Courseware")]
     public class CoursewareInfo
     {
         [DataMember(Name = "LocalId")]
         [PrimaryKey, Column("LocalId"), NotNull]
         public string LocalId { get; set; }

         [DataMember(Name = "RemoteId")]
         [Column("RemoteId")]
         public string RemoteId { get; set; }

         [Column("Name")]
         public string Name { get; set; }
     }

2. 添加DB操作通用类

     public class DbProvider<TDB> where TDB : LinqToDB.Data.DataConnection, new()
     {
         private readonly string _connectionString;
         private readonly Func<string> _getConnectionStringFunc;

         private string ConnectionString
             => string.IsNullOrEmpty(_connectionString) ? _getConnectionStringFunc() : _connectionString;

         public DbProvider(Func<string> getConnectionStringFunc)
         {
             _getConnectionStringFunc = getConnectionStringFunc;
         }
         public TReturn Execute<TReturn>(Func<TDB, TReturn> execute)
         {
             TDB db = null;
             try
             {
                 db = (TDB)Activator.CreateInstance(typeof(TDB), new SQLiteDataProvider(), ConnectionString);
                 return execute(db);
             }
             catch (Exception ex)
             {
                 return default(TReturn);
             }
             finally
             {
                 db?.Dispose();
             }
         }
     }

3. 添加指定数据库的映射连接类

     public partial class CoursewareInfoDb : DataConnection
     {
         public ITable<CoursewareInfo> Coursewares => GetTable<CoursewareInfo>();

         public CoursewareInfoDb()
         {
             InitDataContext();
         }

         public CoursewareInfoDb(string configuration)
             : base(configuration)
         {
             InitDataContext();
         }

         public CoursewareInfoDb(IDataProvider dataProvider, string connectionString)
             : base(dataProvider, connectionString)
         {
             InitDataContext();
         }

         partial void InitDataContext();
     }

4. 添加数据库查询辅助类

这里是将数据库放在程序启动目录下，通过绝对路径引用。

     public class CoursewareSqliteDataReader
     {
         private static readonly string DbName = "CoursewareCacheData.db";
         private readonly DbProvider<CoursewareInfoDb> _coursewareDbProvider;

         public CoursewareSqliteDataReader()
         {
             var dbPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, $"Dbs\\{DbName}");

             if (!File.Exists(dbPath))
             {
                 throw new InvalidOperationException("路径下不存在数据库文件");
             }
             _coursewareDbProvider = new DbProvider<CoursewareInfoDb>(() => $"Data Source={dbPath}");
         }

         public List<CoursewareInfo> GetCoursewares()
         {
             return _coursewareDbProvider.Execute(db => db.Coursewares.ToList());
         }
         public List<CoursewareInfo> GetCoursewares(string queryText)
         {
             return _coursewareDbProvider.Execute(db => db.Coursewares.Where(i=>i.Name.Contains(queryText)).ToList());
         }
     }