PetaPoco的默认映射 拓荒者

PetaPoco的映射需要继承IMapper接口，该接口提供了四个方法：

• TableInfo GetTableInfo(Type pocoType);
• ColumnInfo GetColumnInfo(PropertyInfo pocoProperty);
• Func<object, object> GetFromDbConverter(PropertyInfo TargetProperty, Type SourceType);
• Func<object, object> GetToDbConverter(PropertyInfo SourceProperty);

Brad提供了一个StandardMapper类来实现这个接口，完成PetaPoco中的默认映射。

这个类实现了两个方法：GetTableInfo 和GetColumnInfo，后两个转换的方法均返回null值。

        /// <summary>
        /// Constructs a TableInfo for a POCO by reading its attribute data
        /// </summary>
        /// <param name="pocoType">The POCO Type</param>
        /// <returns></returns>
        public TableInfo GetTableInfo(Type pocoType)
        {
            return TableInfo.FromPoco(pocoType);
        }

        /// <summary>
        /// Constructs a ColumnInfo for a POCO property by reading its attribute data
        /// </summary>
        /// <param name="pocoProperty"></param>
        /// <returns></returns>
        public ColumnInfo GetColumnInfo(PropertyInfo pocoProperty)
        {
            return ColumnInfo.FromProperty(pocoProperty);
        }

通过调用TableInfo的FromPoco静态方法生成一个新的TableInfo类，和通过调用ColumnInfo的FromProperty静态方法生成一个新的ColumnInfo类。接下来我们看看这两个方法：

TableInfo.FromPoco

        /// <summary>
        /// Creates and populates a TableInfo from the attributes of a POCO
        /// </summary>
        /// <param name="t">The POCO type</param>
        /// <returns>A TableInfo instance</returns>
        public static TableInfo FromPoco(Type t)
        {
            TableInfo ti = new TableInfo();

            // Get the table name
            var a = t.GetCustomAttributes(typeof(TableNameAttribute), true);
            ti.TableName = a.Length == 0 ? t.Name : (a[0] as TableNameAttribute).Value;

            // Get the primary key
            a = t.GetCustomAttributes(typeof(PrimaryKeyAttribute), true);
            ti.PrimaryKey = a.Length == 0 ? "ID" : (a[0] as PrimaryKeyAttribute).Value;
            ti.SequenceName = a.Length == 0 ? null : (a[0] as PrimaryKeyAttribute).sequenceName;
            ti.AutoIncrement = a.Length == 0 ? false : (a[0] as PrimaryKeyAttribute).autoIncrement;

            return ti;
        }

这个方法通过反射，得到TableInfo的TableName、PrimaryKey、AutoIncrement等信息。

ColumnInfo.FromProperty

        /// <summary>
        /// Creates and populates a ColumnInfo from the attributes of a POCO property.
        /// </summary>
        /// <param name="pi">The property whose column info is required</param>
        /// <returns>A ColumnInfo instance</returns>
        public static ColumnInfo FromProperty(PropertyInfo pi)
        {
            // Check if declaring poco has [Explicit] attribute
            bool ExplicitColumns = pi.DeclaringType.GetCustomAttributes(typeof(ExplicitColumnsAttribute), true).Length > 0;

            // Check for [Column]/[Ignore] Attributes
            var ColAttrs = pi.GetCustomAttributes(typeof(ColumnAttribute), true);
            if (ExplicitColumns)
            {
                if (ColAttrs.Length == 0)
                    return null;
            }
            else
            {
                if (pi.GetCustomAttributes(typeof(IgnoreAttribute), true).Length != 0)
                    return null;
            }

            ColumnInfo ci = new ColumnInfo();

            // Read attribute
            if (ColAttrs.Length > 0)
            {
                var colattr = (ColumnAttribute)ColAttrs[0];

                ci.ColumnName = colattr.Name==null ? pi.Name : colattr.Name;
                ci.ForceToUtc = colattr.ForceToUtc;
                if ((colattr as ResultColumnAttribute) != null)
                    ci.ResultColumn = true;
            }
            else
            {
                ci.ColumnName = pi.Name;
                ci.ForceToUtc = false;
                ci.ResultColumn = false;
            }

            return ci;
        }

该方法通过反射得到一个属性所对应的字段的信息。

通过这两个方法能够得到实体到数据表的映射关系，在类PocoData和PocoColumn中，将实际的数据通过映射得到具体的实体。