public string TranslateEntityQuery(EntityQueryExpression exp)
{
StringBuilder str = new StringBuilder();
str.Append(this.TranslateSelect(exp));
str.Append(SQL_FROM);
str.Append(DbProvider.BuildTableName(exp.From.GetName()));
if (exp.Joins != null)
{
foreach (var join in exp.Joins)
{
str.Append(this.TranslateJoin(join));
}
}
if (exp.Where != null)
{
str.Append(SQL_WHERE);
str.Append(this.TranslateWhere(exp.Where));
}
if (exp.IsOrderBy)
{
str.Append(this.TranslateOrderyByList(exp.OrderByList));
}
if (exp.GroupBy != null)
{
str.Append(this.TranslateGroupBy(exp.GroupBy));
}
return(str.ToString());
}
public string TranslateSelect(EntityQueryExpression exp)
{
StringBuilder str = new StringBuilder();
str.Append(SQL_SELECT);
if (exp.IsDistinct != null && exp.IsDistinct.Value)
{
str.Append(SQL_DISTINCT);
}
//如果不是 子查询的表达式
if (exp == this.Expression)
{
str.Append(this.DbProvider.GetSQLSelectTopClip(this));
}
var fields = exp.SelectFields;
var appended = false;
foreach (var field in fields)
{
if (appended)
{
str.Append(",");
}
str.Append(field.FullName);
appended = true;
}
if (!appended)
{
str.Append(" *");
}
return(str.ToString());
}
/// <summary>
/// 跳过N行
/// 实现方案： 根据排序和条件检索出全部数据
/// 再加入一个条件：id 大于/或小于(需要根据排序来判断) 前N行记录ID的最大/最小值
/// </summary>
/// <param name="translater"></param>
protected virtual void PrepareSkip(ExpressionTranslater translater)
{
var exp = translater.Expression;
var idField = exp.From.GetIdentityField();
if ((idField as object) == null)
{
throw new NotImplementedException(TextResource.AutoKeyToSearchAllow);
}
var IsIdentityFieldDesc = exp.IsIdentityFieldDesc;
//子查询
var subTableName = "subtable";
var subId = idField.SetTableName(subTableName);
var subTable = DataHelper.Clone(exp.From) as Entity;
subTable.SetAliasName(subTableName);
var subExp = new EntityQueryExpression(subTable);
//前N行记录ID的最大/最小值
if (IsIdentityFieldDesc)
{
subExp.Select = new SelectExpression(new Field[] { subId.Min() });
}
else
{
subExp.Select = new SelectExpression(new Field[] { subId.Max() });
}
//复制条件与排序
subExp.Where = exp.Where.Clone();
subExp.Where.SetTable(subTableName);
subExp.OrderByList = exp.OrderByList.Clone().SetTable(subTableName);
//再加入一个条件：id 大于/或小于(需要根据排序来判断) 前N行记录ID的最大/最小值
var newWhere = WhereExpression.Create(exp.From.GetIdentityField(), subExp,
IsIdentityFieldDesc ? QueryOperator.Less : QueryOperator.Greater);
exp.Where = WhereExpression.Create(exp.Where, newWhere, QueryOperator.And);
}
public ExpressionTranslater(DbProvider dbProvider, EntityQueryExpression exp)
{
this.DbProvider = dbProvider;
this.Params = new List <QueryParameter>();
this.Expression = exp;
}
