/// <summary>
/// 初始化 <see cref="ColumnExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="dbQuery">查询语义</param>
public ColumnExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, IDbQueryableInfo_Select dbQuery)
: base(provider, aliases, dbQuery.Select.Expressions != null ? dbQuery.Select.Expressions[0] : null)
{
_provider = provider;
_aliases = aliases;
_dbQuery = dbQuery;
_groupBy = dbQuery.GroupBy;
_include = dbQuery.Includes;
if (_pickColumns == null)
{
_pickColumns = new DbColumnCollection();
}
_navDescriptors = new NavDescriptorCollection();
_navDescriptorKeys = new List <string>(10);
}
/// <summary>
/// 初始化 <see cref="NpgJoinExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="joins">JOIN 子句</param>
/// <param name="dbExpressionType">表达式类型</param>
public NpgJoinExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, List <DbExpression> joins, DbExpressionType dbExpressionType)
: base(provider, aliases, joins)
{
_qJoin = joins;
_aliases = aliases;
_provider = provider;
_dbExpressionType = dbExpressionType;
if (_dbExpressionType == DbExpressionType.Delete)
{
_keywordName = "USING ";
}
else if (_dbExpressionType == DbExpressionType.Update)
{
_keywordName = "FROM ";
}
_pad = "".PadLeft(_keywordName.Length, ' ');
}
/// <summary>
/// 实例化 <see cref="NpgMappingDbCommand" /> 的新实例
/// </summary>
/// <param name="provider">数据查询提供者</param>
/// <param name="aliases">别名</param>
/// <param name="dbExpressionType">表达式类型</param>
/// <param name="token">解析上下文参数</param>
public NpgMappingDbCommand(IDbQueryProvider provider, TableAlias aliases, DbExpressionType dbExpressionType, ResolveToken token)
: base(provider, aliases, token)
{
_provider = provider;
_aliases = aliases;
_onPhrase = _provider.CreateSqlBuilder(token);
_dbExpressionType = dbExpressionType;
if (_dbExpressionType == DbExpressionType.Delete)
{
_keywordName = "USING ";
}
else if (_dbExpressionType == DbExpressionType.Update)
{
_keywordName = "FROM ";
}
_pad = "".PadLeft(_keywordName.Length, ' ');
}
/// <summary>
/// 生成关联子句所表示的别名列表
/// </summary>
/// <param name="dbQuery">查询语义</param>
/// <param name="token">解析上下文</param>
/// <returns></returns>
protected TableAlias PrepareTableAlias(IDbQueryableInfo_Select dbQuery, ResolveToken token)
{
var aliases = new TableAlias((dbQuery.Joins != null ? dbQuery.Joins.Count : 0) + 1, token != null ? token.AliasPrefix : null);
foreach (DbExpression exp in dbQuery.Joins)
{
// [INNER/LEFT JOIN]
if (exp.DbExpressionType == DbExpressionType.GroupJoin || exp.DbExpressionType == DbExpressionType.Join || exp.DbExpressionType == DbExpressionType.GroupRightJoin)
{
this.PrepareJoinAlias(exp, aliases);
}
else if (exp.DbExpressionType == DbExpressionType.SelectMany)
{
this.PrepareCrossAlias(exp, aliases);
}
}
return(aliases);
}
// Cross Join
private void AppendCrossJoin(ISqlBuilder builder, DbExpression exp, TableAlias aliases)
{
var lambdaExp = exp.Expressions[1] as LambdaExpression;
Type type = lambdaExp.Parameters[1].Type;
var typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(type);
bool withNoLock = !typeRuntime.IsTemporary && _context.NoLock && !string.IsNullOrEmpty(_provider.WidthNoLock);
builder.Append(' ');
builder.AppendMember(typeRuntime.TableName, !typeRuntime.IsTemporary);
string alias = aliases.GetTableAlias(lambdaExp.Parameters[1]);
builder.Append(' ');
builder.Append(alias);
builder.Append(' ');
if (withNoLock)
{
builder.Append(_provider.WidthNoLock);
builder.Append(' ');
}
}
// LEFT OR INNER JOIN
private void AppendLfInJoin(ISqlBuilder builder, DbExpression dbExpression, TableAlias aliases)
{
bool withNoLock = false;
builder.Append(' ');
IDbQueryable dbQuery = (IDbQueryable)((dbExpression.Expressions[0] as ConstantExpression).Value);
if (dbQuery.DbExpressions.Count == 1 && dbQuery.DbExpressions[0].DbExpressionType == DbExpressionType.GetTable)
{
Type type = dbExpression.Expressions[0].Type.GetGenericArguments()[0];
var typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(type);
builder.AppendMember(typeRuntime.TableName, !typeRuntime.IsTemporary);
withNoLock = !typeRuntime.IsTemporary && _context.NoLock && !string.IsNullOrEmpty(_provider.WidthNoLock);
}
else
{
// 嵌套
var cmd = dbQuery.Resolve(builder.Indent + 1, false, builder.Token);
builder.Append("(");
builder.Append(cmd.CommandText);
builder.AppendNewLine();
builder.Append(')');
}
var left = dbExpression.Expressions[1] as LambdaExpression;
var right = dbExpression.Expressions[2] as LambdaExpression;
// t0(t1)
string alias = !(left.Body.NodeType == ExpressionType.New || left.Body.NodeType == ExpressionType.MemberInit)
? aliases.GetTableAlias(dbExpression.Expressions[2])
: aliases.GetTableAlias(right.Parameters[0]);
builder.Append(' ');
builder.Append(alias);
builder.Append(' ');
if (withNoLock)
{
builder.Append(_provider.WidthNoLock);
builder.Append(' ');
}
// ON a.Name = b.Name AND a.Id = b.Id
builder.Append("ON ");
if (left.Body.NodeType == ExpressionType.New)
{
var body1 = left.Body as NewExpression;
var body2 = right.Body as NewExpression;
for (int index = 0; index < body1.Arguments.Count; ++index)
{
builder.AppendMember(aliases, body1.Arguments[index]);
builder.Append(" = ");
builder.AppendMember(aliases, body2.Arguments[index]);
if (index < body1.Arguments.Count - 1)
{
builder.Append(" AND ");
}
}
}
else if (left.Body.NodeType == ExpressionType.MemberInit)
{
var body1 = left.Body as MemberInitExpression;
var body2 = right.Body as MemberInitExpression;
for (int index = 0; index < body1.Bindings.Count; ++index)
{
builder.AppendMember(aliases, (body1.Bindings[index] as MemberAssignment).Expression);
builder.Append(" = ");
builder.AppendMember(aliases, (body2.Bindings[index] as MemberAssignment).Expression);
if (index < body1.Bindings.Count - 1)
{
builder.Append(" AND ");
}
}
}
else
{
builder.AppendMember(aliases, left.Body.ReduceUnary());
builder.Append(" = ");
builder.AppendMember(aliases, right.Body.ReduceUnary());
}
}
/// <summary>
/// 初始化 <see cref="SqlServerJoinExpressionVisitor"/> 类的新实例
/// </summary>
internal SqlServerJoinExpressionVisitor(SqlClient.SqlServerDbContext context, TableAlias aliases, List <DbExpression> joins)
: base(context.Provider, aliases, joins)
{
_joins = joins;
_aliases = aliases;
_context = context;
_provider = context.Provider as SqlClient.SqlServerDbQueryProvider;
}
/// <summary>
/// 初始化 <see cref="NavPredicateExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="predicate">要访问的表达式</param>
/// <param name="alias">指定的表别名</param>
public NavPredicateExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, Expression predicate, string alias)
: base(provider, aliases, predicate)
{
_expression = base.Expression;
_alias = alias;
}
/// <summary>
/// 初始化 <see cref="OracleUpdateExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="expression">要访问的表达式</param>
public OracleUpdateExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, Expression expression)
: base(provider, aliases, expression)
{
_provider = provider;
_aliases = aliases;
}
/// <summary>
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="groupBy">GROUP BY 子句</param>
public GroupByExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, DbExpression groupBy)
: base(provider, aliases, groupBy != null ? groupBy.Expressions[0] : null)
{
}
/// <summary>
/// 初始化 <see cref="OracleColumnExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="dbQuery">查询语义</param>
public OracleColumnExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, IDbQueryableInfo_Select dbQuery)
: base(provider, aliases, dbQuery)
{
_dbQuery = dbQuery;
}
// 获取 LEFT JOIN / INNER JOIN 子句关联表的的别名
private void PrepareJoinAlias(DbExpression dbExpression, TableAlias aliases)
{
Type type = dbExpression.Expressions[0].Type.GetGenericArguments()[0];
string name = TypeRuntimeInfoCache.GetRuntimeInfo(type).TableName;
string outerAlias = null;
// on a.Name equals b.Name 或 on new{ Name = a.Name,Id=a.Id } equals new { Name = b.Name,Id=b.Id }
var left = dbExpression.Expressions[1] as LambdaExpression;
var right = dbExpression.Expressions[2] as LambdaExpression;
if (left.Body.NodeType == ExpressionType.New)
{
var body1 = left.Body as NewExpression;
var body2 = right.Body as NewExpression;
for (int index = 0; index < body1.Arguments.Count; ++index)
{
aliases.GetTableAlias(body1.Arguments[index]);
}
for (int index = 0; index < body2.Arguments.Count; ++index)
{
string alias = aliases.GetTableAlias(body2.Arguments[index]);
outerAlias = alias;
// 记录显示指定的LEFT JOIN 表别名
aliases.AddJoinTableAlias(name, alias);
}
}
else if (left.Body.NodeType == ExpressionType.MemberInit)
{
var body1 = left.Body as MemberInitExpression;
var body2 = right.Body as MemberInitExpression;
for (int index = 0; index < body1.Bindings.Count; ++index)
{
aliases.GetTableAlias((body1.Bindings[index] as MemberAssignment).Expression);
}
for (int index = 0; index < body2.Bindings.Count; ++index)
{
string alias = aliases.GetTableAlias((body2.Bindings[index] as MemberAssignment).Expression);
outerAlias = alias;
// 记录显示指定的LEFT JOIN 表别名
aliases.AddJoinTableAlias(name, alias);
}
}
else
{
aliases.GetTableAlias(dbExpression.Expressions[1]);
string alias = aliases.GetTableAlias(dbExpression.Expressions[2]);
outerAlias = alias;
// 记录显示指定的LEFT JOIN 表别名
aliases.AddJoinTableAlias(name, alias);
}
// 由 GetTable 重载指定的导航属性表别名
if (dbExpression.Expressions.Length > 4)
{
if (string.IsNullOrEmpty(outerAlias) || outerAlias == TableAlias.ALIASNULL)
{
var lambda = dbExpression.Expressions[3] as LambdaExpression;
string alias = aliases.GetTableAlias(lambda.Parameters[1]);
outerAlias = alias;
// 记录显示指定的LEFT JOIN 表别名
aliases.AddJoinTableAlias(name, alias);
}
var member = (dbExpression.Expressions[4] as LambdaExpression).Body as MemberExpression;
string keyId = member.GetKeyWidthoutAnonymous();
// 记录GetTable<,>(path)指定的表别名
aliases.AddGetTableAlias(keyId, outerAlias);
}
}
// 添加导航属性关联
protected override void ResoveNavMember()
{
if (base.NavMembers == null || base.NavMembers.Count == 0)
{
return;
}
// 如果有一对多的导航属性，肯定会产生嵌套查询。那么内层查询别名肯定是t0，所以需要清掉
if (this.HasMany)
{
_aliases = new TableAlias(_aliases.HoldQty);
}
//开始产生LEFT JOIN 子句
ISqlBuilder builder = this.JoinFragment;
foreach (var nav in base.NavMembers)
{
string key = nav.KeyId;
MemberExpression m = nav.Expression;
TypeRuntimeInfo typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(m.Expression.Type);
ForeignKeyAttribute attribute = typeRuntime.GetMemberAttribute <ForeignKeyAttribute>(m.Member.Name);
string innerKey = string.Empty;
string outerKey = key;
string innerAlias = string.Empty;
if (!m.Expression.Visitable())
{
innerKey = m.Expression.NodeType == ExpressionType.Parameter
? (m.Expression as ParameterExpression).Name
: (m.Expression as MemberExpression).Member.Name;
}
else
{
MemberExpression mLeft = null;
if (m.Expression.NodeType == ExpressionType.MemberAccess)
{
mLeft = m.Expression as MemberExpression;
}
else if (m.Expression.NodeType == ExpressionType.Call)
{
mLeft = (m.Expression as MethodCallExpression).Object as MemberExpression;
}
string name = TypeRuntimeInfoCache.GetRuntimeInfo(mLeft.Type).TableName;
innerAlias = _aliases.GetJoinTableAlias(name);
if (string.IsNullOrEmpty(innerAlias))
{
string keyLeft = mLeft.GetKeyWidthoutAnonymous();
if (base.NavMembers.Contains(keyLeft))
{
innerKey = keyLeft;
}
innerAlias = _aliases.GetNavTableAlias(innerKey);
}
}
string alias1 = !string.IsNullOrEmpty(innerAlias) ? innerAlias : _aliases.GetTableAlias(innerKey);
string alias2 = _aliases.GetNavTableAlias(outerKey);
builder.AppendNewLine();
builder.Append("LEFT JOIN ");
Type type = m.Type;
if (type.IsGenericType)
{
type = type.GetGenericArguments()[0];
}
var typeRuntime2 = TypeRuntimeInfoCache.GetRuntimeInfo(type);
builder.AppendMember(typeRuntime2.TableName, !typeRuntime2.IsTemporary);
builder.Append(" ");
builder.Append(alias2);
bool withNoLock = !typeRuntime2.IsTemporary && _context.NoLock && !string.IsNullOrEmpty(_provider.WidthNoLock);
if (withNoLock)
{
builder.Append(' ');
builder.Append(_provider.WidthNoLock);
}
builder.Append(" ON ");
for (int i = 0; i < attribute.InnerKeys.Length; i++)
{
if (attribute.InnerKeys[i].StartsWith(Constant.CONSTANT_FOREIGNKEY, StringComparison.Ordinal))
{
builder.Append(attribute.InnerKeys[i].Substring(7));
}
else
{
builder.Append(alias1);
builder.Append('.');
builder.AppendMember(attribute.InnerKeys[i]);
}
builder.Append(" = ");
if (attribute.OuterKeys[i].StartsWith(Constant.CONSTANT_FOREIGNKEY, StringComparison.Ordinal))
{
builder.Append(attribute.OuterKeys[i].Substring(7));
}
else
{
builder.Append(alias2);
builder.Append('.');
builder.AppendMember(attribute.OuterKeys[i]);
}
if (i < attribute.InnerKeys.Length - 1)
{
builder.Append(" AND ");
}
}
if (nav.Predicate != null)
{
string alias = _aliases.GetNavTableAlias(nav.KeyId);
var visitor = new NavPredicateExpressionVisitor(_provider, _aliases, nav.Predicate, alias);
visitor.Write(builder);
}
}
}
// LEFT OR INNER JOIN
private void AppendLfInJoin(ISqlBuilder jf, ISqlBuilder on, DbExpression dbExpression, TableAlias aliases)
{
IDbQueryable sQuery = (IDbQueryable)((dbExpression.Expressions[0] as ConstantExpression).Value);
if (!usedKeyword)
{
jf.AppendNewLine();
jf.Append(_keywordName);
usedKeyword = true;
}
else
{
jf.Append(',');
jf.AppendNewLine();
jf.Append(_pad);
}
if (sQuery.DbExpressions.Count == 1 && sQuery.DbExpressions[0].DbExpressionType == DbExpressionType.GetTable)
{
Type type = dbExpression.Expressions[0].Type.GetGenericArguments()[0];
var typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(type);
jf.AppendMember(typeRuntime.TableName, !typeRuntime.IsTemporary);
}
else
{
// 嵌套
var cmd = sQuery.Resolve(jf.Indent + _dbExpressionType == DbExpressionType.Delete ? 2 : 1, false, jf.Token);
jf.Append("( ");
jf.Append(_dbExpressionType == DbExpressionType.Delete ? cmd.CommandText.TrimStart() : cmd.CommandText);
jf.Append(')');
}
LambdaExpression left = dbExpression.Expressions[1] as LambdaExpression;
LambdaExpression right = dbExpression.Expressions[2] as LambdaExpression;
// t0(t1)
string alias = !(left.Body.NodeType == ExpressionType.New || left.Body.NodeType == ExpressionType.MemberInit)
? aliases.GetTableAlias(dbExpression.Expressions[2])
: aliases.GetTableAlias(right.Parameters[0]);
jf.Append(' ');
jf.Append(alias);
if (on.Length > 0)
{
on.Append(" AND ");
}
if (left.Body.NodeType == ExpressionType.New)
{
NewExpression body1 = left.Body as NewExpression;
NewExpression body2 = right.Body as NewExpression;
for (int index = 0; index < body1.Arguments.Count; ++index)
{
on.AppendMember(aliases, body1.Arguments[index]);
on.Append(" = ");
on.AppendMember(aliases, body2.Arguments[index]);
if (index < body1.Arguments.Count - 1)
{
on.Append(" AND ");
}
}
}
else if (left.Body.NodeType == ExpressionType.MemberInit)
{
MemberInitExpression body1 = left.Body as MemberInitExpression;
MemberInitExpression body2 = right.Body as MemberInitExpression;
for (int index = 0; index < body1.Bindings.Count; ++index)
{
on.AppendMember(aliases, (body1.Bindings[index] as MemberAssignment).Expression);
on.Append(" = ");
on.AppendMember(aliases, (body2.Bindings[index] as MemberAssignment).Expression);
if (index < body1.Bindings.Count - 1)
{
on.Append(" AND ");
}
}
}
else
{
on.AppendMember(aliases, left.Body.ReduceUnary());
on.Append(" = ");
on.AppendMember(aliases, right.Body.ReduceUnary());
}
}
/// <summary>
/// 追加列名
/// </summary>
/// <param name="expression">列名表达式</param>
/// <param name="aliases">表别名</param>
/// <returns>返回解析到的表别名</returns>
public Expression AppendMember(Expression expression, TableAlias aliases)
{
this.AppendMember(aliases, expression);
return(expression);
}
/// <summary>
/// 初始化 <see cref="NpgWhereExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="dbExpression">要访问的表达式</param>
public NpgWhereExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, DbExpression dbExpression)
: base(provider, aliases, dbExpression)
{
_expression = dbExpression != null && dbExpression.Expressions != null ? dbExpression.Expressions[0] : null;
}
/// <summary>
/// 添加导航属性关联
/// </summary>
protected override void ResoveNavMember()
{
if (this.NavMembers == null || this.NavMembers.Count == 0)
{
return;
}
// 如果有一对多的导航属性，肯定会产生嵌套查询。那么内层查询别名肯定是t0，所以需要清掉
if (this.HasMany)
{
_aliases = new TableAlias(_aliases.HoldQty);
}
//开始产生 USING 子句
ISqlBuilder jf = this.JoinFragment;
int index = -1;
// 未生成USING子句
if (_aliases.HoldQty <= 1)
{
jf.AppendNewLine();
jf.Append(_keywordName);
}
else
{
jf.Append(',');
jf.AppendNewLine();
}
foreach (var nav in this.NavMembers)
{
index++;
string key = nav.KeyId;
MemberExpression m = nav.Expression;
TypeRuntimeInfo typeRuntime = TypeRuntimeInfoCache.GetRuntimeInfo(m.Expression.Type);
ForeignKeyAttribute attribute = typeRuntime.GetMemberAttribute <ForeignKeyAttribute>(m.Member.Name);
string innerKey = string.Empty;
string outerKey = key;
string innerAlias = string.Empty;
if (!m.Expression.Visitable())
{
innerKey = m.Expression.NodeType == ExpressionType.Parameter
? (m.Expression as ParameterExpression).Name
: (m.Expression as MemberExpression).Member.Name;
}
else
{
MemberExpression mLeft = null;
if (m.Expression.NodeType == ExpressionType.MemberAccess)
{
mLeft = m.Expression as MemberExpression;
}
else if (m.Expression.NodeType == ExpressionType.Call)
{
mLeft = (m.Expression as MethodCallExpression).Object as MemberExpression;
}
string name = TypeRuntimeInfoCache.GetRuntimeInfo(mLeft.Type).TableName;
innerAlias = _aliases.GetJoinTableAlias(name);
if (string.IsNullOrEmpty(innerAlias))
{
string keyLeft = mLeft.GetKeyWidthoutAnonymous();
if (this.NavMembers.Contains(keyLeft))
{
innerKey = keyLeft;
}
innerAlias = _aliases.GetNavTableAlias(innerKey);
}
}
string alias1 = !string.IsNullOrEmpty(innerAlias) ? innerAlias : _aliases.GetTableAlias(innerKey);
string alias2 = _aliases.GetNavTableAlias(outerKey);
// 补充与USING字符串同等间距的空白
if (_aliases.HoldQty > 1 || index > 0)
{
jf.Append(_pad);
}
Type type = m.Type;
var typeRumtime2 = TypeRuntimeInfoCache.GetRuntimeInfo(type);
if (type.IsGenericType)
{
type = type.GetGenericArguments()[0];
}
jf.AppendMember(typeRumtime2.TableName, typeRumtime2.IsTemporary);
jf.Append(' ');
jf.Append(alias2);
if (_onPhrase.Length > 0)
{
_onPhrase.Append(" AND ");
}
for (int i = 0; i < attribute.InnerKeys.Length; i++)
{
if (attribute.InnerKeys[i].StartsWith(Constant.CONSTANT_FOREIGNKEY, StringComparison.Ordinal))
{
_onPhrase.Append(attribute.InnerKeys[i].Substring(7));
}
else
{
_onPhrase.Append(alias1);
_onPhrase.Append('.');
_onPhrase.AppendMember(attribute.InnerKeys[i]);
}
_onPhrase.Append(" = ");
if (attribute.OuterKeys[i].StartsWith(Constant.CONSTANT_FOREIGNKEY, StringComparison.Ordinal))
{
_onPhrase.Append(attribute.OuterKeys[i].Substring(7));
}
else
{
_onPhrase.Append(alias2);
_onPhrase.Append('.');
_onPhrase.AppendMember(attribute.OuterKeys[i]);
}
}
if (nav.Predicate != null)
{
string alias = _aliases.GetNavTableAlias(nav.KeyId);
var visitor = new NavPredicateExpressionVisitor(_provider, _aliases, nav.Predicate, alias);
visitor.Write(_onPhrase);
}
if (index < this.NavMembers.Count - 1)
{
jf.Append(',');
jf.AppendNewLine();
}
}
}
/// <summary>
/// 初始化 <see cref="HavingExpressionVisitor"/> 类的新实例
/// </summary>
/// <param name="provider">查询语义提供者</param>
/// <param name="aliases">表别名集合</param>
/// <param name="having">HAVING 子句</param>
/// <param name="groupBy">GROUP BY 子句</param>
public HavingExpressionVisitor(IDbQueryProvider provider, TableAlias aliases, DbExpression having, DbExpression groupBy)
: base(provider, aliases, having != null && having.Expressions != null ? having.Expressions[0] : null)
{
_groupBy = groupBy;
_aliases = aliases;
}