Class QueryHelper

Inheritance
object
QueryHelper
Namespace: LinqToDB.SqlQuery
Assembly: linq2db.dll
Syntax
public static class QueryHelper

Methods

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CanBeEvaluated(IQueryElement, EvaluationContext)

Declaration
public static bool CanBeEvaluated(this IQueryElement expr, EvaluationContext context)
Parameters
Type Name Description
IQueryElement expr
EvaluationContext context
Returns
Type Description
bool
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CanBeEvaluated(IQueryElement, bool)

Declaration
public static bool CanBeEvaluated(this IQueryElement expr, bool withParameters)
Parameters
Type Name Description
IQueryElement expr
bool withParameters
Returns
Type Description
bool
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CanRemoveOrderBy(SelectQuery, SqlProviderFlags, QueryInformation)

Detects when we can remove order

Declaration
public static bool CanRemoveOrderBy(SelectQuery selectQuery, SqlProviderFlags flags, QueryInformation information)
Parameters
Type Name Description
SelectQuery selectQuery
SqlProviderFlags flags
QueryInformation information
Returns
Type Description
bool
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CollectDependencies(IQueryElement, IEnumerable<ISqlTableSource>, HashSet<ISqlExpression>, IEnumerable<IQueryElement>?)

Declaration
public static void CollectDependencies(IQueryElement root, IEnumerable<ISqlTableSource> sources, HashSet<ISqlExpression> found, IEnumerable<IQueryElement>? ignore = null)
Parameters
Type Name Description
IQueryElement root
IEnumerable<ISqlTableSource> sources
HashSet<ISqlExpression> found
IEnumerable<IQueryElement> ignore
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CollectUniqueKeys(ISqlTableSource, bool, List<IList<ISqlExpression>>)

Collects unique keys from different sources.

Declaration
public static void CollectUniqueKeys(ISqlTableSource tableSource, bool includeDistinct, List<IList<ISqlExpression>> knownKeys)
Parameters
Type Name Description
ISqlTableSource tableSource
bool includeDistinct

Flag to include Distinct as unique key.
List<IList<ISqlExpression>> knownKeys

List with found keys.
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CollectUniqueKeys(SqlTableSource, List<IList<ISqlExpression>>)

Collects unique keys from different sources.

Declaration
public static void CollectUniqueKeys(SqlTableSource tableSource, List<IList<ISqlExpression>> knownKeys)
Parameters
Type Name Description
SqlTableSource tableSource
List<IList<ISqlExpression>> knownKeys

List with found keys.
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CollectUsedSources(IQueryElement, HashSet<ISqlTableSource>, IEnumerable<IQueryElement>?)

Declaration
public static void CollectUsedSources(IQueryElement root, HashSet<ISqlTableSource> found, IEnumerable<IQueryElement>? ignore = null)
Parameters
Type Name Description
IQueryElement root
HashSet<ISqlTableSource> found
IEnumerable<IQueryElement> ignore
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ConcatSearchCondition(SqlWhereClause, SqlSearchCondition)

Declaration
public static void ConcatSearchCondition(this SqlWhereClause where, SqlSearchCondition search)
Parameters
Type Name Description
SqlWhereClause where
SqlSearchCondition search
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ContainsAggregationOrWindowFunction(IQueryElement)

Declaration
public static bool ContainsAggregationOrWindowFunction(IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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ContainsAggregationOrWindowFunctionDeep(IQueryElement)

Declaration
public static bool ContainsAggregationOrWindowFunctionDeep(IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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ContainsAggregationOrWindowFunctionOneLevel(IQueryElement)

Declaration
public static bool ContainsAggregationOrWindowFunctionOneLevel(IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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ContainsElement(IQueryElement, IQueryElement)

Declaration
public static bool ContainsElement(IQueryElement testedRoot, IQueryElement element)
Parameters
Type Name Description
IQueryElement testedRoot
IQueryElement element
Returns
Type Description
bool
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ConvertFormatToConcatenation(string, IList<ISqlExpression>)

Declaration
public static ISqlExpression ConvertFormatToConcatenation(string format, IList<ISqlExpression> parameters)
Parameters
Type Name Description
string format
IList<ISqlExpression> parameters
Returns
Type Description
ISqlExpression
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CorrectSearchConditionNesting(SelectQuery, SqlCondition, HashSet<ISqlTableSource>)

Declaration
public static SqlCondition CorrectSearchConditionNesting(SelectQuery sql, SqlCondition condition, HashSet<ISqlTableSource> forTableSources)
Parameters
Type Name Description
SelectQuery sql
SqlCondition condition
HashSet<ISqlTableSource> forTableSources
Returns
Type Description
SqlCondition
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CountElements(ISqlExpression)

Declaration
public static IDictionary<QueryElementType, int> CountElements(ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
IDictionary<QueryElementType, int>
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DependencyCount(IQueryElement, IQueryElement, HashSet<IQueryElement>?)

Declaration
public static int DependencyCount(IQueryElement testedRoot, IQueryElement onElement, HashSet<IQueryElement>? elementsToIgnore = null)
Parameters
Type Name Description
IQueryElement testedRoot
IQueryElement onElement
HashSet<IQueryElement> elementsToIgnore
Returns
Type Description
int
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EnsureConjunction(SqlSearchCondition)

Ensures that expression is not A OR B but (A OR B) Function makes all needed manipulations for that

Declaration
public static SqlSearchCondition EnsureConjunction(this SqlSearchCondition searchCondition)
Parameters
Type Name Description
SqlSearchCondition searchCondition
Returns
Type Description
SqlSearchCondition
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EnsureConjunction(SqlWhereClause)

Ensures that expression is not A OR B but (A OR B) Function makes all needed manipulations for that

Declaration
public static SqlWhereClause EnsureConjunction(this SqlWhereClause whereClause)
Parameters
Type Name Description
SqlWhereClause whereClause
Returns
Type Description
SqlWhereClause
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EnumerateAccessibleSources(SelectQuery)

Enumerates table sources recursively based on joins

Declaration
public static IEnumerable<ISqlTableSource> EnumerateAccessibleSources(SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
Returns
Type Description
IEnumerable<ISqlTableSource>
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EnumerateAccessibleSources(SqlTableSource)

Declaration
public static IEnumerable<ISqlTableSource> EnumerateAccessibleSources(SqlTableSource tableSource)
Parameters
Type Name Description
SqlTableSource tableSource
Returns
Type Description
IEnumerable<ISqlTableSource>
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EnumerateAccessibleTables(SelectQuery)

Declaration
public static IEnumerable<SqlTable> EnumerateAccessibleTables(SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
Returns
Type Description
IEnumerable<SqlTable>
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EnumerateInnerJoined(SelectQuery)

Declaration
public static IEnumerable<SqlTableSource> EnumerateInnerJoined(SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
Returns
Type Description
IEnumerable<SqlTableSource>
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EnumerateInnerJoined(SqlTableSource)

Declaration
public static IEnumerable<SqlTableSource> EnumerateInnerJoined(SqlTableSource tableSource)
Parameters
Type Name Description
SqlTableSource tableSource
Returns
Type Description
IEnumerable<SqlTableSource>
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EnumerateJoins(SelectQuery)

Declaration
public static IEnumerable<SqlJoinedTable> EnumerateJoins(SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
Returns
Type Description
IEnumerable<SqlJoinedTable>
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EnumerateJoins(SqlTableSource)

Declaration
public static IEnumerable<SqlJoinedTable> EnumerateJoins(SqlTableSource tableSource)
Parameters
Type Name Description
SqlTableSource tableSource
Returns
Type Description
IEnumerable<SqlJoinedTable>
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EnumerateLevelSources(SelectQuery)

Declaration
public static IEnumerable<ISqlTableSource> EnumerateLevelSources(SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
Returns
Type Description
IEnumerable<ISqlTableSource>
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EnumerateLevelSources(SqlTableSource)

Declaration
public static IEnumerable<ISqlTableSource> EnumerateLevelSources(SqlTableSource tableSource)
Parameters
Type Name Description
SqlTableSource tableSource
Returns
Type Description
IEnumerable<ISqlTableSource>
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EnumerateLevelTables(SelectQuery)

Declaration
public static IEnumerable<SqlTable> EnumerateLevelTables(SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
Returns
Type Description
IEnumerable<SqlTable>
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EvaluateBoolExpression(IQueryElement, EvaluationContext, bool?)

Declaration
public static bool? EvaluateBoolExpression(this IQueryElement expr, EvaluationContext context, bool? defaultValue = null)
Parameters
Type Name Description
IQueryElement expr
EvaluationContext context
bool? defaultValue
Returns
Type Description
bool?
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EvaluateExpression(IQueryElement, EvaluationContext)

Declaration
public static object? EvaluateExpression(this IQueryElement expr, EvaluationContext context)
Parameters
Type Name Description
IQueryElement expr
EvaluationContext context
Returns
Type Description
object
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ExtractField(ISqlExpression)

Returns SqlField from specific expression. Usually from SqlColumn. Conversion is ignored.

Declaration
public static SqlField? ExtractField(ISqlExpression expression)
Parameters
Type Name Description
ISqlExpression expression
Returns
Type Description
SqlField

Field instance associated with expression
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FindJoin(SelectQuery, Func<SqlJoinedTable, bool>)

Declaration
public static SqlJoinedTable? FindJoin(this SelectQuery query, Func<SqlJoinedTable, bool> match)
Parameters
Type Name Description
SelectQuery query
Func<SqlJoinedTable, bool> match
Returns
Type Description
SqlJoinedTable
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GenerateEquality(ISqlExpression, ISqlExpression, bool)

Declaration
public static SqlCondition GenerateEquality(ISqlExpression field1, ISqlExpression field2, bool compareNullsAsValues)
Parameters
Type Name Description
ISqlExpression field1
ISqlExpression field2
bool compareNullsAsValues
Returns
Type Description
SqlCondition
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GetBoolValue(ISqlExpression, EvaluationContext)

Declaration
public static bool? GetBoolValue(ISqlExpression expression, EvaluationContext context)
Parameters
Type Name Description
ISqlExpression expression
EvaluationContext context
Returns
Type Description
bool?
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GetColumnDescriptor(ISqlExpression?)

Returns ColumnDescriptor for expr.

Declaration
public static ColumnDescriptor? GetColumnDescriptor(ISqlExpression? expr)
Parameters
Type Name Description
ISqlExpression expr

Tested SQL Expression.
Returns
Type Description
ColumnDescriptor

Associated column descriptor or null.
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GetDbDataType(ISqlExpression?)

Declaration
public static DbDataType GetDbDataType(ISqlExpression? expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
DbDataType
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GetDeleteTable(SqlDeleteStatement)

Declaration
public static SqlTable? GetDeleteTable(this SqlDeleteStatement deleteStatement)
Parameters
Type Name Description
SqlDeleteStatement deleteStatement
Returns
Type Description
SqlTable
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GetExpressionType(ISqlExpression)

Declaration
public static DbDataType GetExpressionType(this ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
DbDataType
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GetParameterValue(SqlParameter, IReadOnlyParameterValues?)

Declaration
public static SqlParameterValue GetParameterValue(this SqlParameter parameter, IReadOnlyParameterValues? parameterValues)
Parameters
Type Name Description
SqlParameter parameter
IReadOnlyParameterValues parameterValues
Returns
Type Description
SqlParameterValue
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GetUnderlyingExpression(ISqlExpression?)

Unwraps SqlColumn and returns underlying expression.

Declaration
public static ISqlExpression? GetUnderlyingExpression(ISqlExpression? expression)
Parameters
Type Name Description
ISqlExpression expression
Returns
Type Description
ISqlExpression

Underlying expression.
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GetUnderlyingExpressionValue(SqlExpression, bool)

Declaration
public static ISqlExpression GetUnderlyingExpressionValue(SqlExpression sqlExpression, bool checkNullability)
Parameters
Type Name Description
SqlExpression sqlExpression
bool checkNullability
Returns
Type Description
ISqlExpression
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GetUnderlyingField(ISqlExpression)

Returns SqlField from specific expression. Usually from SqlColumn. Complex expressions ignored.

Declaration
public static SqlField? GetUnderlyingField(ISqlExpression expression)
Parameters
Type Name Description
ISqlExpression expression
Returns
Type Description
SqlField

Field instance associated with expression
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GetUpdateTable(SqlUpdateStatement)

Declaration
public static SqlTable? GetUpdateTable(this SqlUpdateStatement updateStatement)
Parameters
Type Name Description
SqlUpdateStatement updateStatement
Returns
Type Description
SqlTable
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GetUsedSources(ISqlExpression, HashSet<ISqlTableSource>)

Retrieves which sources are used in the rootexpression

Declaration
public static void GetUsedSources(ISqlExpression root, HashSet<ISqlTableSource> foundSources)
Parameters
Type Name Description
ISqlExpression root

Expression to analyze.
HashSet<ISqlTableSource> foundSources

Output container for detected sources/
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GetValueConverter(ISqlExpression?)

Returns IValueConverter for expr.

Declaration
public static IValueConverter? GetValueConverter(ISqlExpression? expr)
Parameters
Type Name Description
ISqlExpression expr

Tested SQL Expression.
Returns
Type Description
IValueConverter

Associated converter or null.
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HasOuterReferences(ISet<ISqlTableSource>, ISqlExpression)

Declaration
public static bool HasOuterReferences(ISet<ISqlTableSource> sources, ISqlExpression expr)
Parameters
Type Name Description
ISet<ISqlTableSource> sources
ISqlExpression expr
Returns
Type Description
bool
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HasQueryParameters(ISqlExpression)

Declaration
public static bool HasQueryParameters(ISqlExpression expression)
Parameters
Type Name Description
ISqlExpression expression
Returns
Type Description
bool
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IsAggregationFunction(IQueryElement)

Declaration
public static bool IsAggregationFunction(IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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IsAggregationOrWindowFunction(IQueryElement)

Declaration
public static bool IsAggregationOrWindowFunction(IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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IsComplexExpression(ISqlExpression)

Declaration
public static bool IsComplexExpression(this ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
bool
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IsConstant(ISqlExpression)

Returns true if tested expression is constant during query execution (e.g. value or parameter).

Declaration
public static bool IsConstant(ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr

Tested expression.
Returns
Type Description
bool
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IsConstantFast(ISqlExpression)

Declaration
public static bool IsConstantFast(ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
bool
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IsDependsOn(IQueryElement, IQueryElement, HashSet<IQueryElement>?)

Declaration
public static bool IsDependsOn(IQueryElement testedRoot, IQueryElement onElement, HashSet<IQueryElement>? elementsToIgnore = null)
Parameters
Type Name Description
IQueryElement testedRoot
IQueryElement onElement
HashSet<IQueryElement> elementsToIgnore
Returns
Type Description
bool
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IsDependsOn(IQueryElement, HashSet<ISqlTableSource>, HashSet<IQueryElement>?)

Declaration
public static bool IsDependsOn(IQueryElement testedRoot, HashSet<ISqlTableSource> onSources, HashSet<IQueryElement>? elementsToIgnore = null)
Parameters
Type Name Description
IQueryElement testedRoot
HashSet<ISqlTableSource> onSources
HashSet<IQueryElement> elementsToIgnore
Returns
Type Description
bool
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IsEqualTables(SqlTable?, SqlTable?)

Declaration
public static bool IsEqualTables(SqlTable? table1, SqlTable? table2)
Parameters
Type Name Description
SqlTable table1
SqlTable table2
Returns
Type Description
bool
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IsExpression(ISqlExpression)

Returns true if it is anything except Field or Column.

Declaration
public static bool IsExpression(ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr

Tested expression
Returns
Type Description
bool

true if tested expression is not a Field or Column
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IsMutable(IQueryElement)

Declaration
public static bool IsMutable(this IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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IsTransitiveExpression(SqlExpression, bool)

Declaration
public static bool IsTransitiveExpression(SqlExpression sqlExpression, bool checkNullability)
Parameters
Type Name Description
SqlExpression sqlExpression
bool checkNullability
Returns
Type Description
bool
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IsWindowFunction(IQueryElement)

Declaration
public static bool IsWindowFunction(IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
bool
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JoinRemoval<TContext>(TContext, SqlStatement, Func<TContext, SqlStatement, SqlJoinedTable, bool>)

Removes Join from query based on joinFunc result.

Declaration
public static SqlStatement JoinRemoval<TContext>(TContext context, SqlStatement statement, Func<TContext, SqlStatement, SqlJoinedTable, bool> joinFunc)
Parameters
Type Name Description
TContext context

joinFunc context object.
SqlStatement statement

Source statement.
Func<TContext, SqlStatement, SqlJoinedTable, bool> joinFunc
Returns
Type Description
SqlStatement

Same or new statement with removed joins.
Type Parameters
Name Description
TContext
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MoveOrderByUp(params SelectQuery[])

Helper function for moving Ordering up in select tree.

Declaration
public static void MoveOrderByUp(params SelectQuery[] queries)
Parameters
Type Name Description
SelectQuery[] queries

Array of queries
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MoveSearchConditionsToJoin(SelectQuery, SqlJoinedTable, List<SqlCondition>?)

Declaration
public static void MoveSearchConditionsToJoin(SelectQuery sql, SqlJoinedTable joinedTable, List<SqlCondition>? movedConditions)
Parameters
Type Name Description
SelectQuery sql
SqlJoinedTable joinedTable
List<SqlCondition> movedConditions
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NeedColumnForExpression(SelectQuery, ISqlExpression, bool)

Returns correct column or field according to nesting.

Declaration
public static ISqlExpression? NeedColumnForExpression(SelectQuery selectQuery, ISqlExpression forExpression, bool inProjection)
Parameters
Type Name Description
SelectQuery selectQuery

Analyzed query.
ISqlExpression forExpression

Expression that has to be enveloped by column.
bool inProjection

If 'true', function ensures that column is created. If 'false' it may return Field if it fits to nesting level.
Returns
Type Description
ISqlExpression

Returns Column of Field according to its nesting level. May return null if expression is not valid for selectQuery
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NeedParameterInlining(ISqlExpression)

Declaration
public static bool NeedParameterInlining(ISqlExpression expression)
Parameters
Type Name Description
ISqlExpression expression
Returns
Type Description
bool
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RemoveNotUnusedColumns(SelectQuery)

Declaration
public static void RemoveNotUnusedColumns(this SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery
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RootQuery(SelectQuery)

Declaration
public static SelectQuery RootQuery(this SelectQuery query)
Parameters
Type Name Description
SelectQuery query
Returns
Type Description
SelectQuery
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ShouldCheckForNull(ISqlExpression)

Declaration
public static bool ShouldCheckForNull(this ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
bool
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SuggestDbDataType(ISqlExpression)

Declaration
public static DbDataType? SuggestDbDataType(ISqlExpression expr)
Parameters
Type Name Description
ISqlExpression expr
Returns
Type Description
DbDataType?
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ToDebugString(IQueryElement)

Declaration
public static string ToDebugString(this IQueryElement expr)
Parameters
Type Name Description
IQueryElement expr
Returns
Type Description
string
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TransformExpressionIndexes<TContext>(TContext, string, Func<TContext, int, int>)

Declaration
public static string TransformExpressionIndexes<TContext>(TContext context, string expression, Func<TContext, int, int> transformFunc)
Parameters
Type Name Description
TContext context
string expression
Func<TContext, int, int> transformFunc
Returns
Type Description
string
Type Parameters
Name Description
TContext
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TransformInnerJoinsToWhere(SelectQuery)

Transforms SELECT * FROM A INNER JOIN B ON A.ID = B.ID to SELECT * FROM A, B WHERE A.ID = B.ID

Declaration
public static SelectQuery TransformInnerJoinsToWhere(this SelectQuery selectQuery)
Parameters
Type Name Description
SelectQuery selectQuery

Input SelectQuery.
Returns
Type Description
SelectQuery

The same query instance.
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TryConvertOrderedDistinctToGroupBy(SelectQuery, SqlProviderFlags)

Converts ORDER BY DISTINCT to GROUP BY equivalent

Declaration
public static bool TryConvertOrderedDistinctToGroupBy(SelectQuery select, SqlProviderFlags flags)
Parameters
Type Name Description
SelectQuery select
SqlProviderFlags flags
Returns
Type Description
bool
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TryEvaluateExpression(IQueryElement, EvaluationContext, out object?)

Declaration
public static bool TryEvaluateExpression(this IQueryElement expr, EvaluationContext context, out object? result)
Parameters
Type Name Description
IQueryElement expr
EvaluationContext context
object result
Returns
Type Description
bool
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TryRemoveDistinct(SelectQuery, QueryInformation)

Detects when we can remove order

Declaration
public static bool TryRemoveDistinct(SelectQuery selectQuery, QueryInformation information)
Parameters
Type Name Description
SelectQuery selectQuery
QueryInformation information
Returns
Type Description
bool
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UnwrapExpression(ISqlExpression, bool)

Declaration
public static ISqlExpression UnwrapExpression(ISqlExpression expr, bool checkNullability)
Parameters
Type Name Description
ISqlExpression expr
bool checkNullability
Returns
Type Description
ISqlExpression
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ValidateTable(SelectQuery, ISqlTableSource)

Declaration
public static bool ValidateTable(SelectQuery selectQuery, ISqlTableSource table)
Parameters
Type Name Description
SelectQuery selectQuery
ISqlTableSource table
Returns
Type Description
bool
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WrapQuery<TStatement>(TStatement, SelectQuery, bool)

Wraps queryToWrap by another select. Keeps columns count the same. After modification statement is equivalent symantically.

--before
SELECT c1, c2
FROM A
-- after
SELECT B.c1, B.c2
FROM (
  SELECT c1, c2
  FROM A
     ) B
Declaration
public static TStatement WrapQuery<TStatement>(TStatement statement, SelectQuery queryToWrap, bool allowMutation) where TStatement : SqlStatement
Parameters
Type Name Description
TStatement statement

Statement which may contain tested query
SelectQuery queryToWrap

Tells which select query needs enveloping
bool allowMutation

Wrapped query can be not recreated for performance considerations.
Returns
Type Description
TStatement

The same statement or modified statement when wrapping has been performed.
Type Parameters
Name Description
TStatement
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WrapQuery<TStatement, TContext>(TContext, TStatement, Func<TContext, SelectQuery, IQueryElement?, bool>, Action<TContext, SelectQuery, SelectQuery>?, bool, bool)

Wraps queries by another select. Keeps columns count the same. After modification statement is equivalent symantically.

Declaration
public static TStatement WrapQuery<TStatement, TContext>(TContext context, TStatement statement, Func<TContext, SelectQuery, IQueryElement?, bool> wrapTest, Action<TContext, SelectQuery, SelectQuery>? onWrap, bool allowMutation, bool withStack) where TStatement : SqlStatement
Parameters
Type Name Description
TContext context

onWrap and wrapTest context object.
TStatement statement
Func<TContext, SelectQuery, IQueryElement, bool> wrapTest

Delegate for testing when query needs to be wrapped.
Action<TContext, SelectQuery, SelectQuery> onWrap

After enveloping query this function called for prcess needed optimizations.
bool allowMutation

Wrapped query can be not recreated for performance considerations.
bool withStack

Must be set to true, if wrapTest function use 3rd parameter (containing parent element) otherwise it will be always null.
Returns
Type Description
TStatement

The same statement or modified statement when wrapping has been performed.
Type Parameters
Name Description
TStatement
TContext

Type of onWrap and wrapTest context object.
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WrapQuery<TStatement, TContext>(TContext, TStatement, Func<TContext, SelectQuery, IQueryElement?, int>, Action<TContext, IReadOnlyList<SelectQuery>>, bool, bool)

Wraps tested query in subquery(s). Keeps columns count the same. After modification statement is equivalent semantically.

--before
SELECT c1, c2           -- QA
FROM A
-- after (with 2 subqueries)
SELECT C.c1, C.c2       -- QC
FROM (
  SELECT B.c1, B.c2     -- QB
  FROM (
    SELECT c1, c2       -- QA
    FROM A
       ) B
  FROM
     ) C
Declaration
public static TStatement WrapQuery<TStatement, TContext>(TContext context, TStatement statement, Func<TContext, SelectQuery, IQueryElement?, int> wrapTest, Action<TContext, IReadOnlyList<SelectQuery>> onWrap, bool allowMutation, bool withStack) where TStatement : SqlStatement
Parameters
Type Name Description
TContext context

onWrap and wrapTest context object.
TStatement statement

Statement which may contain tested query
Func<TContext, SelectQuery, IQueryElement, int> wrapTest

Delegate for testing which query needs to be enveloped. Result of delegate call tells how many subqueries needed. 0 - no changes 1 - one subquery N - N subqueries
Action<TContext, IReadOnlyList<SelectQuery>> onWrap

After wrapping query this function called for prcess needed optimizations. Array of queries contains [QC, QB, QA]
bool allowMutation

Wrapped query can be not recreated for performance considerations.
bool withStack

Must be set to true, if wrapTest function use 3rd parameter (containing parent element) otherwise it will be always null.
Returns
Type Description
TStatement

The same statement or modified statement when wrapping has been performed.
Type Parameters
Name Description
TStatement
TContext

Type of onWrap and wrapTest context object.