Simple.Data

Simple.Data defines a number of commands for retrieving data from a data store. These can then be daisychained in a LINQ-like fashion with further methods to modify the basic query.

ExistsBy

ExistsBy returns a boolean value based on whether a search returns any values based on at least one column name and value to filter by. AnyBy is a synonym for ExistsBy.

There are two ways to form a ExistsBy method.

You can specify the column names as named parameters.
You can specify the column names as part of the method

Syntax

public bool ExistsBy(
		Object[] filterExpressions
	)

public bool ExistsBycolumnName1[AndcolumnName2…](
	Object columnValue1
	[, Object columnValue2]
)

Parameters

filterExpressions: Type: object[]
A set of named parameters where the parameter name is that of column being filtered against and the parameter value is that which the column should equal.
columnName1[, columnName2, …, columnNameX]: Type: string The name of the column(s) being filtered against
columnValue1[, columnValue2, …, columnValueX]: Type: object (typically string or int) columnValueY contains the value with which column with name columnNameY should equal.

Return Value

Type: bool
A value indicating whether records exists in the table that satisfy the given conditions.

Exceptions

Exception	Condition
`UnresolvableObjectException`	`ExistsBy` is called on a table that doesn’t exist
`ArgumentException`	The number of `columnValues` does not match the number of `columnNames` or no arguments at all have been passed to the method.
`FormatException`	The type of a `columnValue` does not match the actual type of the corresponding `columnName`

Note that issues #318, #319, and #320 are still open with regards to exceptions thrown by ExistsBy.

Remarks

ExistsBy is used to determine whether data exists in a table based on a set of criteria where the value of columns in a row

are equal to given values - e.g. GenreId=6 and Title="Nevermind"
are within certain sets of values, a range or an array. See the Where clause page for more information

If you wish to include a column name in a filter that contains the string “and” in it, you must use the named parameter form of ExistsBy. If you have a column called, for example, HandlingCode, and you try to call

ExistsByHandlingCode(1);

the parser will split that into two columns, H & lingCode, and throw an ArgumentException. So you have to use the named parameter form for columns with “and” in the name. For example,

ExistsBy(HandlingCode:1);

Examples

One Criteria

The following example returns true if there are any records in the Albums table with GenreId equal to 1.

bool albumExists = Database.Open().Albums.ExistsByGenreId(1);
	
// The named parameter equivalent call to ExistsBy() is
// bool albumExists = Database.Open().Albums.ExistsBy(GenreId:1);

// Also equivalent are
// bool albumExists = Database.Open().Albums.AnyByGenreId(1);
// bool albumExists = Database.Open().Albums.AnyBy(GenreId:1);

Simple.Data sends the following SQL to the database when albumExists is evaluated.

select DISTINCT 1 from [dbo].[Albums]  
WHERE 
   [dbo].[Albums].[GenreId] = @p1
@p1 (Int32) = 1

Two Criteria

The following example returns true if there are any records in the Albums table with GenreId equal to 1 and ArtistId equal to 120.

bool albumExists = Database.Open().Albums.ExistsByGenreIdAndArtistId(1,120);
	
// The named parameter equivalent call to ExistsBy() is
// bool albumExists = Database.Open().Albums.ExistsBy(GenreId:1,ArtistId:120);

// Also equivalent are
// bool albumExists = Database.Open().Albums.AnyByGenreIdAndArtistId(1,120);
// bool albumExists = Database.Open().Albums.AnyBy(GenreId:1,ArtistId:120);

Simple.Data sends the following SQL to the database when albumExists is evaluated.

select DISTINCT 1 from [dbo].[Albums] 
WHERE 
    ([dbo].[Albums].[GenreId] = @p1 AND [dbo].[Albums].[ArtistId] = @p2)
@p1 (Int32) = 1
@p2 (Int32) = 120