/// <summary>
/// 尝试将 exp 转换成 DbParameterExpression。
/// </summary>
/// <param name="exp"></param>
/// <returns></returns>
public static DbExpression ParseDbExpression(this DbExpression exp)
{
DbExpression stripedExp = DbExpressionHelper.StripInvalidConvert(exp);
DbExpression tempExp = stripedExp;
List <DbConvertExpression> cList = null;
while (tempExp.NodeType == DbExpressionType.Convert)
{
if (cList == null)
{
cList = new List <DbConvertExpression>();
}
DbConvertExpression c = (DbConvertExpression)tempExp;
cList.Add(c);
tempExp = c.Operand;
}
if (tempExp.NodeType == DbExpressionType.Constant || tempExp.NodeType == DbExpressionType.Parameter)
{
return(stripedExp);
}
if (tempExp.NodeType == DbExpressionType.MemberAccess)
{
DbMemberExpression dbMemberExp = (DbMemberExpression)tempExp;
if (ExistDateTime_NowOrDateTime_UtcNow(dbMemberExp))
{
return(stripedExp);
}
DbParameterExpression val;
if (DbExpressionExtensions.TryParseToParameterExpression(dbMemberExp, out val))
{
if (cList != null)
{
if (val.Value == DBNull.Value)//如果是 null，则不需要 Convert 了，在数据库里没意义
{
return(val);
}
DbConvertExpression c = null;
for (int i = cList.Count - 1; i > -1; i--)
{
DbConvertExpression item = cList[i];
c = new DbConvertExpression(item.Type, val);
}
return(c);
}
return(val);
}
}
return(stripedExp);
}
public override DbExpression Visit(DbConvertExpression exp)
{
DbExpression stripedExp = DbExpressionHelper.StripInvalidConvert(exp);
if (stripedExp.NodeType != DbExpressionType.Convert)
{
stripedExp.Accept(this);
return(exp);
}
exp = (DbConvertExpression)stripedExp;
string dbTypeString;
if (TryGetCastTargetDbTypeString(exp.Operand.Type, exp.Type, out dbTypeString, false))
{
this.BuildCastState(exp.Operand, dbTypeString);
}
else
{
Type targetUnType = Utils.GetUnderlyingType(exp.Type);
if (targetUnType == UtilConstants.TypeOfDateTime)
{
/* DATETIME('2016-08-06 09:01:24') */
this._sqlBuilder.Append("DATETIME(");
exp.Operand.Accept(this);
this._sqlBuilder.Append(")");
}
else
{
exp.Operand.Accept(this);
}
}
return(exp);
}