protected virtual SqlFragment VisitBinaryExpression(DbExpression left, DbExpression right, string op)
{
// Optimization: try to use 'like' instead of 'locate' (Edm.IndexOf) for these
// cases: (like 'word%'), (like '%word') & (like '%word%').
LikeFragment like = TryPromoteToLike(left, right, op);
if (like != null)
{
return(like);
}
// normal flow
BinaryFragment f = new BinaryFragment();
f.Operator = op;
f.Left = left.Accept(this);
f.WrapLeft = ShouldWrapExpression(left);
f.Right = right.Accept(this);
f.WrapRight = ShouldWrapExpression(right);
// Optimization, try to promote to In expression
// NOTE: In EF6, this optimization is already done, we just implement Visit(DbInExpression).
#if !EF6
return(TryToPromoteToIn(f));
#else
return(f);
#endif
}
public override SqlFragment Visit(DbLikeExpression expression)
{
LikeFragment f = new LikeFragment();
f.Argument = expression.Argument.Accept(this);
f.Pattern = expression.Pattern.Accept(this);
return(f);
}
public override SqlFragment Visit(DbLikeExpression expression)
{
LikeFragment f = new LikeFragment();
f.Argument = expression.Argument.Accept(this);
f.Pattern = expression.Pattern.Accept(this);
if (expression.Escape.ExpressionKind != DbExpressionKind.Null)
{
f.Escape = expression.Escape.Accept(this);
}
return(f);
}
public void Visit(LikeFragment f)
{
}
public void Visit(LikeFragment f)
{
}
/// <summary>
/// Examines a binary expression to see if it is an special case suitable to conversion
/// to a more efficient and equivalent LIKE sql expression.
/// </summary>
/// <param name="left"></param>
/// <param name="right"></param>
/// <param name="op"></param>
/// <returns></returns>
protected LikeFragment TryPromoteToLike(DbExpression left, DbExpression right, string op)
{
DbFunctionExpression fl = left as DbFunctionExpression;
if ((fl != null) && (right is DbConstantExpression))
{
LikeFragment like = new LikeFragment();
if (fl.Function.FullName == "Edm.IndexOf")
{
int value = Convert.ToInt32(((DbConstantExpression)right).Value);
like.Argument = fl.Arguments[1].Accept(this);
if ((value == 1) && (op == "="))
{
DbFunctionExpression fr1;
DbFunctionExpression fr2;
if ((fl.Arguments[0] is DbConstantExpression))
{
// Case LIKE 'pattern%'
DbConstantExpression c = (DbConstantExpression)fl.Arguments[0];
like.Pattern = new LiteralFragment(string.Format("'{0}%'", c.Value.ToString().Replace("'", "''")));
return(like);
}
else if ((fl.Arguments.Count == 2) &&
((fr1 = fl.Arguments[0] as DbFunctionExpression) != null) &&
((fr2 = fl.Arguments[1] as DbFunctionExpression) != null) &&
(fr1.Function.FullName == "Edm.Reverse") &&
(fr2.Function.FullName == "Edm.Reverse"))
{
// Case LIKE '%pattern' in EF .NET 4.0
if (fr1.Arguments[0] is DbConstantExpression)
{
DbConstantExpression c = (DbConstantExpression)fr1.Arguments[0];
like.Pattern = new LiteralFragment(string.Format("'%{0}'", c.Value.ToString().Replace("'", "''")));
like.Argument = fr2.Arguments[0].Accept(this);
return(like);
}
}
}
else if (value == 0)
{
if ((op == ">") && (fl.Arguments[0] is DbConstantExpression))
{
// Case LIKE '%pattern%'
DbConstantExpression c = (DbConstantExpression)fl.Arguments[0];
like.Pattern = new LiteralFragment(string.Format("'%{0}%'", c.Value.ToString().Replace("'", "''")));
return(like);
}
}
}
// Like '%pattern' in EF .NET 3.5 (yes, is different than in .NET 4.0)
else if (fl.Function.FullName == "Edm.Right")
{
DbFunctionExpression fLength = fl.Arguments[1] as DbFunctionExpression;
if ((fLength != null) && (fLength.Function.FullName == "Edm.Length") && (fLength.Arguments[0] is DbConstantExpression))
{
DbConstantExpression c2 = fLength.Arguments[0] as DbConstantExpression;
DbConstantExpression c1 = (DbConstantExpression)right;
if (c1.Value == c2.Value)
{
like.Argument = fl.Arguments[0].Accept(this);
like.Pattern = new LiteralFragment(string.Format("'%{0}'", c1.Value));
return(like);
}
}
}
}
return(null);
}
